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 $62.64   3.109%   $64.5875   $64.59   $64.60   $64.60  
  Purchase #2 $119.86   6.239%   $127.3381   $127.34   $127.35   $127.30  
  Purchase #3 $150.88   7.327%   $161.935   $161.94   $161.95   $161.90  
  Purchase #4 $6.91   13.659%   $7.8538   $7.85   $7.85   $7.90  
  Purchase #5 $66.88   13.616%   $75.9864   $75.99   $76.00   $76.00  
  Purchase #6 $215.35   4.467%   $224.9697   $224.97   $224.95   $225.00  
  Purchase #7 $246.99   5.282%   $260.036   $260.04   $260.05   $260.00  
  7 purchase totals = $869.51       $922.7065   $922.72   $922.75   $922.70