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 $30.49   4.196%   $31.7694   $31.77   $31.75   $31.80  
  Purchase #2 $105.51   4.658%   $110.4247   $110.42   $110.40   $110.40  
  Purchase #3 $21.69   13.355%   $24.5867   $24.59   $24.60   $24.60  
  Purchase #4 $84.97   11.545%   $94.7798   $94.78   $94.80   $94.80  
  Purchase #5 $80.86   11.262%   $89.9665   $89.97   $89.95   $90.00  
  Purchase #6 $90.98   6.813%   $97.1785   $97.18   $97.20   $97.20  
  Purchase #7 $180.37   13.340%   $204.4314   $204.43   $204.45   $204.40  
  7 purchase totals = $594.87       $653.1370   $653.14   $653.15   $653.20