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 $84.81   13.283%   $96.0753   $96.08   $96.10   $96.10  
  Purchase #2 $66.81   10.173%   $73.6066   $73.61   $73.60   $73.60  
  Purchase #3 $200.82   7.664%   $216.2108   $216.21   $216.20   $216.20  
  Purchase #4 $35.51   5.355%   $37.4116   $37.41   $37.40   $37.40  
  Purchase #5 $180.28   9.652%   $197.6806   $197.68   $197.70   $197.70  
  Purchase #6 $14.43   9.786%   $15.8421   $15.84   $15.85   $15.80  
  Purchase #7 $139.26   6.400%   $148.1726   $148.17   $148.15   $148.20  
  7 purchase totals = $721.92       $784.9996   $785.00   $785.00   $785.00