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 $58.42   3.141%   $60.255   $60.26   $60.25   $60.30  
  Purchase #2 $123.85   9.140%   $135.1699   $135.17   $135.15   $135.20  
  Purchase #3 $92.46   4.135%   $96.2832   $96.28   $96.30   $96.30  
  Purchase #4 $197.61   5.154%   $207.7948   $207.79   $207.80   $207.80  
  Purchase #5 $189.41   11.289%   $210.7925   $210.79   $210.80   $210.80  
  Purchase #6 $246.55   11.466%   $274.8194   $274.82   $274.80   $274.80  
  Purchase #7 $231.96   12.847%   $261.7599   $261.76   $261.75   $261.80  
  7 purchase totals = $1,140.26       $1,246.8747   $1,246.87   $1,246.85   $1,247.00