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 $60.83   5.552%   $64.2073   $64.21   $64.20   $64.20  
  Purchase #2 $96.41   11.540%   $107.5357   $107.54   $107.55   $107.50  
  Purchase #3 $76.96   4.535%   $80.4501   $80.45   $80.45   $80.50  
  Purchase #4 $111.87   11.275%   $124.4833   $124.48   $124.50   $124.50  
  Purchase #5 $185.88   5.320%   $195.7688   $195.77   $195.75   $195.80  
  Purchase #6 $31.30   12.867%   $35.3274   $35.33   $35.35   $35.30  
  Purchase #7 $178.41   10.430%   $197.0182   $197.02   $197.00   $197.00  
  7 purchase totals = $741.66       $804.7908   $804.80   $804.80   $804.80