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 $64.55   9.594%   $70.7429   $70.74   $70.75   $70.70  
  Purchase #2 $172.34   13.284%   $195.2336   $195.23   $195.25   $195.20  
  Purchase #3 $26.39   12.767%   $29.7592   $29.76   $29.75   $29.80  
  Purchase #4 $46.28   11.817%   $51.7489   $51.75   $51.75   $51.70  
  Purchase #5 $69.47   5.158%   $73.0533   $73.05   $73.05   $73.10  
  Purchase #6 $221.79   3.120%   $228.7098   $228.71   $228.70   $228.70  
  Purchase #7 $225.63   13.133%   $255.262   $255.26   $255.25   $255.30  
  7 purchase totals = $826.45       $904.5097   $904.50   $904.50   $904.50