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 $228.70   9.732%   $250.9571   $250.96   $250.95   $251.00  
  Purchase #2 $33.29   10.727%   $36.861   $36.86   $36.85   $36.90  
  Purchase #3 $69.99   9.328%   $76.5187   $76.52   $76.50   $76.50  
  Purchase #4 $193.87   4.437%   $202.472   $202.47   $202.45   $202.50  
  Purchase #5 $115.84   3.463%   $119.8515   $119.85   $119.85   $119.90  
  Purchase #6 $176.69   3.429%   $182.7487   $182.75   $182.75   $182.70  
  Purchase #7 $68.88   9.821%   $75.6447   $75.64   $75.65   $75.60  
  7 purchase totals = $887.26       $945.0537   $945.05   $945.00   $945.10