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 $239.55   10.547%   $264.8153   $264.82   $264.80   $264.80  
  Purchase #2 $154.29   5.398%   $162.6186   $162.62   $162.60   $162.60  
  Purchase #3 $34.38   3.593%   $35.6153   $35.62   $35.60   $35.60  
  Purchase #4 $241.75   13.205%   $273.6731   $273.67   $273.65   $273.70  
  Purchase #5 $48.82   11.835%   $54.5978   $54.60   $54.60   $54.60  
  Purchase #6 $12.99   5.658%   $13.725   $13.73   $13.75   $13.70  
  Purchase #7 $137.45   10.831%   $152.3372   $152.34   $152.35   $152.30  
  7 purchase totals = $869.23       $957.3823   $957.40   $957.35   $957.30