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 $61.35   9.791%   $67.3568   $67.36   $67.35   $67.40  
  Purchase #2 $156.48   4.327%   $163.2509   $163.25   $163.25   $163.30  
  Purchase #3 $156.68   13.842%   $178.3676   $178.37   $178.35   $178.40  
  Purchase #4 $16.98   6.843%   $18.1419   $18.14   $18.15   $18.10  
  Purchase #5 $14.43   6.854%   $15.419   $15.42   $15.40   $15.40  
  Purchase #6 $217.50   4.716%   $227.7573   $227.76   $227.75   $227.80  
  Purchase #7 $249.87   8.863%   $272.016   $272.02   $272.00   $272.00  
  7 purchase totals = $873.29       $942.3095   $942.32   $942.25   $942.40