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 $38.69   6.770%   $41.3093   $41.31   $41.30   $41.30  
  Purchase #2 $173.43   6.862%   $185.3308   $185.33   $185.35   $185.30  
  Purchase #3 $24.49   7.140%   $26.2386   $26.24   $26.25   $26.20  
  Purchase #4 $117.62   13.459%   $133.4505   $133.45   $133.45   $133.50  
  Purchase #5 $83.78   13.771%   $95.3173   $95.32   $95.30   $95.30  
  Purchase #6 $140.51   5.684%   $148.4966   $148.50   $148.50   $148.50  
  Purchase #7 $24.42   3.857%   $25.3619   $25.36   $25.35   $25.40  
  7 purchase totals = $602.94       $655.5050   $655.51   $655.50   $655.50