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 $63.67   5.742%   $67.3259   $67.33   $67.35   $67.30  
  Purchase #2 $234.88   13.422%   $266.4056   $266.41   $266.40   $266.40  
  Purchase #3 $49.65   10.176%   $54.7024   $54.70   $54.70   $54.70  
  Purchase #4 $196.35   10.874%   $217.7011   $217.70   $217.70   $217.70  
  Purchase #5 $122.97   5.796%   $130.0973   $130.10   $130.10   $130.10  
  Purchase #6 $162.90   13.136%   $184.2985   $184.30   $184.30   $184.30  
  Purchase #7 $25.89   7.866%   $27.9265   $27.93   $27.95   $27.90  
  7 purchase totals = $856.31       $948.4573   $948.47   $948.50   $948.40