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 $35.87   6.117%   $38.0642   $38.06   $38.05   $38.10  
  Purchase #2 $230.48   10.166%   $253.9106   $253.91   $253.90   $253.90  
  Purchase #3 $104.35   8.712%   $113.441   $113.44   $113.45   $113.40  
  Purchase #4 $116.92   8.483%   $126.8383   $126.84   $126.85   $126.80  
  Purchase #5 $163.54   3.400%   $169.1004   $169.10   $169.10   $169.10  
  Purchase #6 $31.78   5.333%   $33.4748   $33.47   $33.45   $33.50  
  Purchase #7 $46.50   8.119%   $50.2753   $50.28   $50.30   $50.30  
  7 purchase totals = $729.44       $785.1046   $785.10   $785.10   $785.10