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 $205.35   10.251%   $226.4004   $226.40   $226.40   $226.40  
  Purchase #2 $202.53   7.128%   $216.9663   $216.97   $216.95   $217.00  
  Purchase #3 $114.90   10.144%   $126.5555   $126.56   $126.55   $126.60  
  Purchase #4 $30.85   5.739%   $32.6205   $32.62   $32.60   $32.60  
  Purchase #5 $126.74   9.824%   $139.1909   $139.19   $139.20   $139.20  
  Purchase #6 $131.77   8.509%   $142.9823   $142.98   $143.00   $143.00  
  Purchase #7 $67.89   6.415%   $72.2451   $72.25   $72.25   $72.20  
  7 purchase totals = $880.03       $956.9610   $956.97   $956.95   $957.00