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 $41.53   5.803%   $43.94   $43.94   $43.95   $43.90  
  Purchase #2 $88.75   3.629%   $91.9707   $91.97   $91.95   $92.00  
  Purchase #3 $207.82   11.186%   $231.0667   $231.07   $231.05   $231.10  
  Purchase #4 $84.63   3.345%   $87.4609   $87.46   $87.45   $87.50  
  Purchase #5 $229.89   6.501%   $244.8351   $244.84   $244.85   $244.80  
  Purchase #6 $65.75   13.568%   $74.671   $74.67   $74.65   $74.70  
  Purchase #7 $156.67   3.756%   $162.5545   $162.55   $162.55   $162.60  
  7 purchase totals = $875.04       $936.4989   $936.50   $936.45   $936.60