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 $90.25   4.146%   $93.9918   $93.99   $94.00   $94.00  
  Purchase #2 $212.76   13.269%   $240.9911   $240.99   $241.00   $241.00  
  Purchase #3 $190.51   3.462%   $197.1055   $197.11   $197.10   $197.10  
  Purchase #4 $124.34   8.439%   $134.8331   $134.83   $134.85   $134.80  
  Purchase #5 $197.75   7.575%   $212.7296   $212.73   $212.75   $212.70  
  Purchase #6 $169.62   13.859%   $193.1276   $193.13   $193.15   $193.10  
  Purchase #7 $121.97   11.756%   $136.3088   $136.31   $136.30   $136.30  
  7 purchase totals = $1,107.20       $1,209.0875   $1,209.09   $1,209.15   $1,209.00