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 $20.91   4.690%   $21.8907   $21.89   $21.90   $21.90  
  Purchase #2 $170.44   5.628%   $180.0324   $180.03   $180.05   $180.00  
  Purchase #3 $54.71   7.728%   $58.938   $58.94   $58.95   $58.90  
  Purchase #4 $109.62   6.128%   $116.3375   $116.34   $116.35   $116.30  
  Purchase #5 $85.34   3.189%   $88.0615   $88.06   $88.05   $88.10  
  Purchase #6 $93.58   11.439%   $104.2846   $104.28   $104.30   $104.30  
  Purchase #7 $205.79   6.550%   $219.2692   $219.27   $219.25   $219.30  
  7 purchase totals = $740.39       $788.8139   $788.81   $788.85   $788.80