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 $215.41   11.244%   $239.6307   $239.63   $239.65   $239.60  
  Purchase #2 $204.83   13.385%   $232.2465   $232.25   $232.25   $232.20  
  Purchase #3 $96.54   11.689%   $107.8246   $107.82   $107.80   $107.80  
  Purchase #4 $111.29   6.523%   $118.5494   $118.55   $118.55   $118.50  
  Purchase #5 $209.87   4.119%   $218.5145   $218.51   $218.50   $218.50  
  Purchase #6 $49.74   6.203%   $52.8254   $52.83   $52.85   $52.80  
  Purchase #7 $41.54   9.366%   $45.4306   $45.43   $45.45   $45.40  
  7 purchase totals = $929.22       $1,015.0217   $1,015.02   $1,015.05   $1,014.80