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 $77.80   8.767%   $84.6207   $84.62   $84.60   $84.60  
  Purchase #2 $222.92   4.541%   $233.0428   $233.04   $233.05   $233.00  
  Purchase #3 $136.48   10.854%   $151.2935   $151.29   $151.30   $151.30  
  Purchase #4 $89.29   13.390%   $101.2459   $101.25   $101.25   $101.20  
  Purchase #5 $205.62   13.321%   $233.0106   $233.01   $233.00   $233.00  
  Purchase #6 $233.28   5.394%   $245.8631   $245.86   $245.85   $245.90  
  Purchase #7 $130.83   12.129%   $146.6984   $146.70   $146.70   $146.70  
  7 purchase totals = $1,096.22       $1,195.7750   $1,195.77   $1,195.75   $1,195.70