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 $232.74   12.472%   $261.7673   $261.77   $261.75   $261.80  
  Purchase #2 $68.60   4.530%   $71.7076   $71.71   $71.70   $71.70  
  Purchase #3 $29.79   10.838%   $33.0186   $33.02   $33.00   $33.00  
  Purchase #4 $133.68   5.255%   $140.7049   $140.70   $140.70   $140.70  
  Purchase #5 $184.30   6.135%   $195.6068   $195.61   $195.60   $195.60  
  Purchase #6 $34.54   5.387%   $36.4007   $36.40   $36.40   $36.40  
  Purchase #7 $19.96   5.858%   $21.1293   $21.13   $21.15   $21.10  
  7 purchase totals = $703.61       $760.3352   $760.34   $760.30   $760.30