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 $52.34   4.796%   $54.8502   $54.85   $54.85   $54.90  
  Purchase #2 $13.73   4.216%   $14.3089   $14.31   $14.30   $14.30  
  Purchase #3 $77.87   4.197%   $81.1382   $81.14   $81.15   $81.10  
  Purchase #4 $98.72   7.147%   $105.7755   $105.78   $105.80   $105.80  
  Purchase #5 $237.90   10.351%   $262.525   $262.53   $262.55   $262.50  
  Purchase #6 $119.73   13.690%   $136.121   $136.12   $136.10   $136.10  
  Purchase #7 $178.97   12.427%   $201.2106   $201.21   $201.20   $201.20  
  7 purchase totals = $779.26       $855.9294   $855.94   $855.95   $855.90