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 $91.65   10.473%   $101.2485   $101.25   $101.25   $101.20  
  Purchase #2 $185.99   9.853%   $204.3156   $204.32   $204.30   $204.30  
  Purchase #3 $160.83   3.387%   $166.2773   $166.28   $166.30   $166.30  
  Purchase #4 $150.98   11.771%   $168.7519   $168.75   $168.75   $168.80  
  Purchase #5 $193.62   5.471%   $204.213   $204.21   $204.20   $204.20  
  Purchase #6 $14.86   3.587%   $15.393   $15.39   $15.40   $15.40  
  Purchase #7 $159.30   4.738%   $166.8476   $166.85   $166.85   $166.80  
  7 purchase totals = $957.23       $1,027.0469   $1,027.05   $1,027.05   $1,027.00