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 $49.29   4.543%   $51.5292   $51.53   $51.55   $51.50  
  Purchase #2 $178.86   8.439%   $193.954   $193.95   $193.95   $194.00  
  Purchase #3 $200.37   7.456%   $215.3096   $215.31   $215.30   $215.30  
  Purchase #4 $160.96   10.193%   $177.3667   $177.37   $177.35   $177.40  
  Purchase #5 $143.55   3.106%   $148.0087   $148.01   $148.00   $148.00  
  Purchase #6 $194.28   13.352%   $220.2203   $220.22   $220.20   $220.20  
  Purchase #7 $47.39   11.861%   $53.0109   $53.01   $53.00   $53.00  
  7 purchase totals = $974.70       $1,059.3994   $1,059.40   $1,059.35   $1,059.40