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 $66.81   13.535%   $75.8527   $75.85   $75.85   $75.90  
  Purchase #2 $230.51   7.415%   $247.6023   $247.60   $247.60   $247.60  
  Purchase #3 $63.82   7.659%   $68.708   $68.71   $68.70   $68.70  
  Purchase #4 $159.54   5.785%   $168.7694   $168.77   $168.75   $168.80  
  Purchase #5 $92.67   12.134%   $103.9146   $103.91   $103.90   $103.90  
  Purchase #6 $133.25   11.466%   $148.5284   $148.53   $148.55   $148.50  
  Purchase #7 $133.45   11.679%   $149.0356   $149.04   $149.05   $149.00  
  7 purchase totals = $880.05       $962.4110   $962.41   $962.40   $962.40