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 $54.62   9.443%   $59.7778   $59.78   $59.80   $59.80  
  Purchase #2 $56.53   10.188%   $62.2893   $62.29   $62.30   $62.30  
  Purchase #3 $198.69   4.196%   $207.027   $207.03   $207.05   $207.00  
  Purchase #4 $234.95   10.317%   $259.1898   $259.19   $259.20   $259.20  
  Purchase #5 $113.61   9.401%   $124.2905   $124.29   $124.30   $124.30  
  Purchase #6 $61.91   13.852%   $70.4858   $70.49   $70.50   $70.50  
  Purchase #7 $46.90   10.817%   $51.9732   $51.97   $51.95   $52.00  
  7 purchase totals = $767.21       $835.0334   $835.04   $835.10   $835.10