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 $173.39   12.340%   $194.7863   $194.79   $194.80   $194.80  
  Purchase #2 $60.38   5.691%   $63.8162   $63.82   $63.80   $63.80  
  Purchase #3 $105.77   10.158%   $116.5141   $116.51   $116.50   $116.50  
  Purchase #4 $120.56   7.607%   $129.731   $129.73   $129.75   $129.70  
  Purchase #5 $45.61   6.243%   $48.4574   $48.46   $48.45   $48.50  
  Purchase #6 $20.53   13.170%   $23.2338   $23.23   $23.25   $23.20  
  Purchase #7 $116.33   11.106%   $129.2496   $129.25   $129.25   $129.20  
  7 purchase totals = $642.57       $705.7884   $705.79   $705.80   $705.70