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 $71.37   8.135%   $77.1759   $77.18   $77.20   $77.20  
  Purchase #2 $168.38   8.137%   $182.0811   $182.08   $182.10   $182.10  
  Purchase #3 $83.67   12.834%   $94.4082   $94.41   $94.40   $94.40  
  Purchase #4 $199.75   9.620%   $218.966   $218.97   $218.95   $219.00  
  Purchase #5 $119.53   11.262%   $132.9915   $132.99   $133.00   $133.00  
  Purchase #6 $96.61   9.498%   $105.786   $105.79   $105.80   $105.80  
  Purchase #7 $111.33   13.175%   $125.9977   $126.00   $126.00   $126.00  
  7 purchase totals = $850.64       $937.4064   $937.42   $937.45   $937.50