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 $207.98   7.510%   $223.5993   $223.60   $223.60   $223.60  
  Purchase #2 $59.97   10.804%   $66.4492   $66.45   $66.45   $66.40  
  Purchase #3 $43.42   10.715%   $48.0725   $48.07   $48.05   $48.10  
  Purchase #4 $164.94   13.680%   $187.5038   $187.50   $187.50   $187.50  
  Purchase #5 $207.57   8.498%   $225.2093   $225.21   $225.20   $225.20  
  Purchase #6 $154.61   5.469%   $163.0656   $163.07   $163.05   $163.10  
  Purchase #7 $39.81   5.213%   $41.8853   $41.89   $41.90   $41.90  
  7 purchase totals = $878.30       $955.7850   $955.79   $955.75   $955.80