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 $54.87   8.375%   $59.4654   $59.47   $59.45   $59.50  
  Purchase #2 $209.93   12.204%   $235.5499   $235.55   $235.55   $235.50  
  Purchase #3 $213.63   6.421%   $227.3472   $227.35   $227.35   $227.30  
  Purchase #4 $122.79   13.251%   $139.0609   $139.06   $139.05   $139.10  
  Purchase #5 $77.36   8.653%   $84.054   $84.05   $84.05   $84.10  
  Purchase #6 $119.66   13.496%   $135.8093   $135.81   $135.80   $135.80  
  Purchase #7 $82.71   8.737%   $89.9364   $89.94   $89.95   $89.90  
  7 purchase totals = $880.95       $971.2231   $971.23   $971.20   $971.20