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 $157.74   6.681%   $168.2786   $168.28   $168.30   $168.30  
  Purchase #2 $142.91   3.288%   $147.6089   $147.61   $147.60   $147.60  
  Purchase #3 $35.76   11.168%   $39.7537   $39.75   $39.75   $39.80  
  Purchase #4 $209.57   3.445%   $216.7897   $216.79   $216.80   $216.80  
  Purchase #5 $158.71   5.160%   $166.8994   $166.90   $166.90   $166.90  
  Purchase #6 $48.88   5.315%   $51.478   $51.48   $51.50   $51.50  
  Purchase #7 $15.47   4.303%   $16.1357   $16.14   $16.15   $16.10  
  7 purchase totals = $769.04       $806.9440   $806.95   $807.00   $807.00