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 $116.68   6.535%   $124.305   $124.31   $124.30   $124.30  
  Purchase #2 $32.79   6.598%   $34.9535   $34.95   $34.95   $35.00  
  Purchase #3 $153.98   4.383%   $160.7289   $160.73   $160.75   $160.70  
  Purchase #4 $20.67   12.173%   $23.1862   $23.19   $23.20   $23.20  
  Purchase #5 $205.78   6.362%   $218.8717   $218.87   $218.85   $218.90  
  Purchase #6 $217.62   10.365%   $240.1763   $240.18   $240.20   $240.20  
  Purchase #7 $12.34   8.391%   $13.3754   $13.38   $13.40   $13.40  
  7 purchase totals = $759.86       $815.5970   $815.61   $815.65   $815.70