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 $105.50   13.497%   $119.7393   $119.74   $119.75   $119.70  
  Purchase #2 $20.63   10.332%   $22.7615   $22.76   $22.75   $22.80  
  Purchase #3 $129.35   11.698%   $144.4814   $144.48   $144.50   $144.50  
  Purchase #4 $171.66   12.467%   $193.0609   $193.06   $193.05   $193.10  
  Purchase #5 $101.93   6.117%   $108.1651   $108.17   $108.15   $108.20  
  Purchase #6 $241.42   11.328%   $268.7681   $268.77   $268.75   $268.80  
  Purchase #7 $66.78   11.385%   $74.3829   $74.38   $74.40   $74.40  
  7 purchase totals = $837.27       $931.3592   $931.36   $931.35   $931.50