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 $94.88   13.524%   $107.7116   $107.71   $107.70   $107.70  
  Purchase #2 $91.26   12.492%   $102.6602   $102.66   $102.65   $102.70  
  Purchase #3 $178.63   6.843%   $190.8537   $190.85   $190.85   $190.90  
  Purchase #4 $185.72   3.549%   $192.3112   $192.31   $192.30   $192.30  
  Purchase #5 $221.37   6.629%   $236.0446   $236.04   $236.05   $236.00  
  Purchase #6 $7.75   8.761%   $8.429   $8.43   $8.45   $8.40  
  Purchase #7 $221.72   3.702%   $229.9281   $229.93   $229.95   $229.90  
  7 purchase totals = $1,001.33       $1,067.9384   $1,067.93   $1,067.95   $1,067.90