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 $59.60   10.349%   $65.768   $65.77   $65.75   $65.80  
  Purchase #2 $27.38   10.580%   $30.2768   $30.28   $30.30   $30.30  
  Purchase #3 $226.71   7.621%   $243.9876   $243.99   $244.00   $244.00  
  Purchase #4 $17.55   12.655%   $19.771   $19.77   $19.75   $19.80  
  Purchase #5 $217.27   11.492%   $242.2387   $242.24   $242.25   $242.20  
  Purchase #6 $107.38   8.293%   $116.285   $116.29   $116.30   $116.30  
  Purchase #7 $232.57   9.840%   $255.4549   $255.45   $255.45   $255.50  
  7 purchase totals = $888.46       $973.7820   $973.79   $973.80   $973.90