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 $91.30   5.122%   $95.9764   $95.98   $96.00   $96.00  
  Purchase #2 $112.79   3.151%   $116.344   $116.34   $116.35   $116.30  
  Purchase #3 $183.66   5.514%   $193.787   $193.79   $193.80   $193.80  
  Purchase #4 $71.79   5.809%   $75.9603   $75.96   $75.95   $76.00  
  Purchase #5 $92.49   13.363%   $104.8494   $104.85   $104.85   $104.80  
  Purchase #6 $80.38   12.717%   $90.6019   $90.60   $90.60   $90.60  
  Purchase #7 $42.99   13.472%   $48.7816   $48.78   $48.80   $48.80  
  7 purchase totals = $675.40       $726.3006   $726.30   $726.35   $726.30