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 $48.39   10.253%   $53.3514   $53.35   $53.35   $53.40  
  Purchase #2 $58.53   13.187%   $66.2484   $66.25   $66.25   $66.20  
  Purchase #3 $78.78   6.595%   $83.9755   $83.98   $84.00   $84.00  
  Purchase #4 $172.76   9.247%   $188.7351   $188.74   $188.75   $188.70  
  Purchase #5 $229.48   13.239%   $259.8609   $259.86   $259.85   $259.90  
  Purchase #6 $188.54   8.212%   $204.0229   $204.02   $204.00   $204.00  
  Purchase #7 $186.56   9.258%   $203.8317   $203.83   $203.85   $203.80  
  7 purchase totals = $963.04       $1,060.0259   $1,060.03   $1,060.05   $1,060.00