Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.61   12.141%   $267.5796   $267.58   $267.60   $267.60  
  Purchase #2 $167.74   8.298%   $181.6591   $181.66   $181.65   $181.70  
  Purchase #3 $178.36   3.864%   $185.2518   $185.25   $185.25   $185.30  
  Purchase #4 $204.84   10.873%   $227.1123   $227.11   $227.10   $227.10  
  Purchase #5 $226.93   11.739%   $253.5693   $253.57   $253.55   $253.60  
  Purchase #6 $220.29   9.506%   $241.2308   $241.23   $241.25   $241.20  
  Purchase #7 $114.28   13.801%   $130.0518   $130.05   $130.05   $130.10  
  7 purchase totals = $1,351.05       $1,486.4547   $1,486.45   $1,486.45   $1,486.60