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 $62.60   13.165%   $70.8413   $70.84   $70.85   $70.80  
  Purchase #2 $177.34   13.476%   $201.2383   $201.24   $201.25   $201.20  
  Purchase #3 $146.60   13.575%   $166.501   $166.50   $166.50   $166.50  
  Purchase #4 $16.38   11.457%   $18.2567   $18.26   $18.25   $18.30  
  Purchase #5 $35.27   6.249%   $37.474   $37.47   $37.45   $37.50  
  Purchase #6 $84.61   9.283%   $92.4643   $92.46   $92.45   $92.50  
  Purchase #7 $104.73   10.847%   $116.0901   $116.09   $116.10   $116.10  
  7 purchase totals = $627.53       $702.8657   $702.86   $702.85   $702.90