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 $83.68   11.327%   $93.1584   $93.16   $93.15   $93.20  
  Purchase #2 $212.95   11.581%   $237.6117   $237.61   $237.60   $237.60  
  Purchase #3 $102.90   6.806%   $109.9034   $109.90   $109.90   $109.90  
  Purchase #4 $116.60   11.212%   $129.6732   $129.67   $129.65   $129.70  
  Purchase #5 $229.62   8.838%   $249.9138   $249.91   $249.90   $249.90  
  Purchase #6 $114.71   6.798%   $122.508   $122.51   $122.50   $122.50  
  Purchase #7 $100.60   5.381%   $106.0133   $106.01   $106.00   $106.00  
  7 purchase totals = $961.06       $1,048.7818   $1,048.77   $1,048.70   $1,048.80