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 $61.90   6.443%   $65.8882   $65.89   $65.90   $65.90  
  Purchase #2 $107.50   7.600%   $115.67   $115.67   $115.65   $115.70  
  Purchase #3 $105.55   8.256%   $114.2642   $114.26   $114.25   $114.30  
  Purchase #4 $171.72   13.812%   $195.438   $195.44   $195.45   $195.40  
  Purchase #5 $115.28   8.580%   $125.171   $125.17   $125.15   $125.20  
  Purchase #6 $96.50   6.325%   $102.6036   $102.60   $102.60   $102.60  
  Purchase #7 $32.94   9.532%   $36.0798   $36.08   $36.10   $36.10  
  7 purchase totals = $691.39       $755.1148   $755.11   $755.10   $755.20