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 $55.30   8.623%   $60.0685   $60.07   $60.05   $60.10  
  Purchase #2 $191.29   13.151%   $216.4465   $216.45   $216.45   $216.40  
  Purchase #3 $111.66   5.618%   $117.9331   $117.93   $117.95   $117.90  
  Purchase #4 $101.50   8.417%   $110.0433   $110.04   $110.05   $110.00  
  Purchase #5 $41.57   5.403%   $43.816   $43.82   $43.80   $43.80  
  Purchase #6 $188.31   7.340%   $202.132   $202.13   $202.15   $202.10  
  Purchase #7 $68.60   10.142%   $75.5574   $75.56   $75.55   $75.60  
  7 purchase totals = $758.23       $825.9968   $826.00   $826.00   $825.90