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 $10.50   7.551%   $11.2929   $11.29   $11.30   $11.30  
  Purchase #2 $18.76   4.280%   $19.5629   $19.56   $19.55   $19.60  
  Purchase #3 $219.67   10.328%   $242.3575   $242.36   $242.35   $242.40  
  Purchase #4 $35.78   10.108%   $39.3966   $39.40   $39.40   $39.40  
  Purchase #5 $21.77   6.599%   $23.2066   $23.21   $23.20   $23.20  
  Purchase #6 $178.65   5.296%   $188.1113   $188.11   $188.10   $188.10  
  Purchase #7 $195.28   10.818%   $216.4054   $216.41   $216.40   $216.40  
  7 purchase totals = $680.41       $740.3332   $740.34   $740.30   $740.40