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 $49.35   3.567%   $51.1103   $51.11   $51.10   $51.10  
  Purchase #2 $240.36   4.242%   $250.5561   $250.56   $250.55   $250.60  
  Purchase #3 $144.85   6.244%   $153.8944   $153.89   $153.90   $153.90  
  Purchase #4 $166.63   12.342%   $187.1955   $187.20   $187.20   $187.20  
  Purchase #5 $195.63   9.250%   $213.7258   $213.73   $213.75   $213.70  
  Purchase #6 $118.45   11.630%   $132.2257   $132.23   $132.25   $132.20  
  Purchase #7 $203.96   7.484%   $219.2244   $219.22   $219.20   $219.20  
  7 purchase totals = $1,119.23       $1,207.9322   $1,207.94   $1,207.95   $1,207.90