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 $184.96   10.568%   $204.5066   $204.51   $204.50   $204.50  
  Purchase #2 $194.71   10.224%   $214.6172   $214.62   $214.60   $214.60  
  Purchase #3 $191.32   13.359%   $216.8784   $216.88   $216.90   $216.90  
  Purchase #4 $69.87   12.140%   $78.3522   $78.35   $78.35   $78.40  
  Purchase #5 $245.72   4.753%   $257.3991   $257.40   $257.40   $257.40  
  Purchase #6 $92.46   9.584%   $101.3214   $101.32   $101.30   $101.30  
  Purchase #7 $182.67   3.695%   $189.4197   $189.42   $189.40   $189.40  
  7 purchase totals = $1,161.71       $1,262.4946   $1,262.50   $1,262.45   $1,262.50