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 $237.55   10.513%   $262.5236   $262.52   $262.50   $262.50  
  Purchase #2 $17.38   7.177%   $18.6274   $18.63   $18.65   $18.60  
  Purchase #3 $165.89   13.702%   $188.6202   $188.62   $188.60   $188.60  
  Purchase #4 $21.87   13.396%   $24.7997   $24.80   $24.80   $24.80  
  Purchase #5 $184.93   11.688%   $206.5446   $206.54   $206.55   $206.50  
  Purchase #6 $41.96   7.178%   $44.9719   $44.97   $44.95   $45.00  
  Purchase #7 $206.29   5.429%   $217.4895   $217.49   $217.50   $217.50  
  7 purchase totals = $875.87       $963.5769   $963.57   $963.55   $963.50