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 $195.41   4.736%   $204.6646   $204.66   $204.65   $204.70  
  Purchase #2 $236.78   10.779%   $262.3025   $262.30   $262.30   $262.30  
  Purchase #3 $189.35   6.536%   $201.7259   $201.73   $201.75   $201.70  
  Purchase #4 $90.92   13.745%   $103.417   $103.42   $103.40   $103.40  
  Purchase #5 $221.72   12.523%   $249.486   $249.49   $249.50   $249.50  
  Purchase #6 $112.58   10.770%   $124.7049   $124.70   $124.70   $124.70  
  Purchase #7 $162.71   7.108%   $174.2754   $174.28   $174.30   $174.30  
  7 purchase totals = $1,209.47       $1,320.5763   $1,320.58   $1,320.60   $1,320.60