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 $24.63   11.164%   $27.3797   $27.38   $27.40   $27.40  
  Purchase #2 $223.89   13.117%   $253.2577   $253.26   $253.25   $253.30  
  Purchase #3 $117.35   5.286%   $123.5531   $123.55   $123.55   $123.60  
  Purchase #4 $208.63   13.368%   $236.5197   $236.52   $236.50   $236.50  
  Purchase #5 $133.45   5.814%   $141.2088   $141.21   $141.20   $141.20  
  Purchase #6 $39.27   10.366%   $43.3407   $43.34   $43.35   $43.30  
  Purchase #7 $125.74   11.832%   $140.6176   $140.62   $140.60   $140.60  
  7 purchase totals = $872.96       $965.8773   $965.88   $965.85   $965.90