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 $48.92   6.504%   $52.1018   $52.10   $52.10   $52.10  
  Purchase #2 $227.55   9.174%   $248.4254   $248.43   $248.45   $248.40  
  Purchase #3 $144.65   10.172%   $159.3638   $159.36   $159.35   $159.40  
  Purchase #4 $145.91   12.230%   $163.7548   $163.75   $163.75   $163.80  
  Purchase #5 $157.54   6.371%   $167.5769   $167.58   $167.60   $167.60  
  Purchase #6 $220.39   6.835%   $235.4537   $235.45   $235.45   $235.50  
  Purchase #7 $250.85   6.103%   $266.1594   $266.16   $266.15   $266.20  
  7 purchase totals = $1,195.81       $1,292.8358   $1,292.83   $1,292.85   $1,293.00