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 $208.98   13.287%   $236.7472   $236.75   $236.75   $236.70  
  Purchase #2 $84.41   10.254%   $93.0654   $93.07   $93.05   $93.10  
  Purchase #3 $188.42   13.122%   $213.1445   $213.14   $213.15   $213.10  
  Purchase #4 $197.89   6.548%   $210.8478   $210.85   $210.85   $210.80  
  Purchase #5 $84.58   12.810%   $95.4147   $95.41   $95.40   $95.40  
  Purchase #6 $205.50   9.387%   $224.7903   $224.79   $224.80   $224.80  
  Purchase #7 $152.79   5.494%   $161.1843   $161.18   $161.20   $161.20  
  7 purchase totals = $1,122.57       $1,235.1942   $1,235.19   $1,235.20   $1,235.10