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 $66.97   11.552%   $74.7064   $74.71   $74.70   $74.70  
  Purchase #2 $208.87   10.520%   $230.8431   $230.84   $230.85   $230.80  
  Purchase #3 $178.44   4.208%   $185.9488   $185.95   $185.95   $185.90  
  Purchase #4 $238.41   13.379%   $270.3069   $270.31   $270.30   $270.30  
  Purchase #5 $25.98   11.833%   $29.0542   $29.05   $29.05   $29.10  
  Purchase #6 $38.63   6.551%   $41.1607   $41.16   $41.15   $41.20  
  Purchase #7 $152.92   7.238%   $163.9883   $163.99   $164.00   $164.00  
  7 purchase totals = $910.22       $996.0084   $996.01   $996.00   $996.00