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 $168.67   11.814%   $188.5967   $188.60   $188.60   $188.60  
  Purchase #2 $47.74   4.866%   $50.063   $50.06   $50.05   $50.10  
  Purchase #3 $32.46   11.495%   $36.1913   $36.19   $36.20   $36.20  
  Purchase #4 $213.62   10.851%   $236.7999   $236.80   $236.80   $236.80  
  Purchase #5 $94.28   9.164%   $102.9198   $102.92   $102.90   $102.90  
  Purchase #6 $143.72   12.200%   $161.2538   $161.25   $161.25   $161.30  
  Purchase #7 $17.98   10.199%   $19.8138   $19.81   $19.80   $19.80  
  7 purchase totals = $718.47       $795.6383   $795.63   $795.60   $795.70