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 $67.39   13.719%   $76.6352   $76.64   $76.65   $76.60  
  Purchase #2 $213.93   10.667%   $236.7499   $236.75   $236.75   $236.70  
  Purchase #3 $250.28   7.207%   $268.3177   $268.32   $268.30   $268.30  
  Purchase #4 $104.56   5.705%   $110.5251   $110.53   $110.55   $110.50  
  Purchase #5 $60.96   11.625%   $68.0466   $68.05   $68.05   $68.00  
  Purchase #6 $142.47   4.808%   $149.32   $149.32   $149.30   $149.30  
  Purchase #7 $155.68   7.497%   $167.3513   $167.35   $167.35   $167.40  
  7 purchase totals = $995.27       $1,076.9458   $1,076.96   $1,076.95   $1,076.80