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 $57.46   8.861%   $62.5515   $62.55   $62.55   $62.60  
  Purchase #2 $66.63   13.396%   $75.5558   $75.56   $75.55   $75.60  
  Purchase #3 $143.61   5.341%   $151.2802   $151.28   $151.30   $151.30  
  Purchase #4 $174.52   11.361%   $194.3472   $194.35   $194.35   $194.30  
  Purchase #5 $225.49   8.128%   $243.8178   $243.82   $243.80   $243.80  
  Purchase #6 $129.48   9.193%   $141.3831   $141.38   $141.40   $141.40  
  Purchase #7 $79.47   13.644%   $90.3129   $90.31   $90.30   $90.30  
  7 purchase totals = $876.66       $959.2485   $959.25   $959.25   $959.30