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 $48.82   10.138%   $53.7694   $53.77   $53.75   $53.80  
  Purchase #2 $133.97   7.268%   $143.7069   $143.71   $143.70   $143.70  
  Purchase #3 $95.82   6.354%   $101.9084   $101.91   $101.90   $101.90  
  Purchase #4 $81.99   6.692%   $87.4768   $87.48   $87.50   $87.50  
  Purchase #5 $76.25   13.507%   $86.5491   $86.55   $86.55   $86.50  
  Purchase #6 $93.29   10.837%   $103.3998   $103.40   $103.40   $103.40  
  Purchase #7 $159.88   9.182%   $174.5602   $174.56   $174.55   $174.60  
  7 purchase totals = $690.02       $751.3706   $751.38   $751.35   $751.40