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 $96.97   4.266%   $101.1067   $101.11   $101.10   $101.10  
  Purchase #2 $217.81   11.108%   $242.0043   $242.00   $242.00   $242.00  
  Purchase #3 $5.69   3.780%   $5.9051   $5.91   $5.90   $5.90  
  Purchase #4 $247.34   6.600%   $263.6644   $263.66   $263.65   $263.70  
  Purchase #5 $77.94   6.620%   $83.0996   $83.10   $83.10   $83.10  
  Purchase #6 $195.26   5.628%   $206.2492   $206.25   $206.25   $206.20  
  Purchase #7 $51.25   3.798%   $53.1965   $53.20   $53.20   $53.20  
  7 purchase totals = $892.26       $955.2258   $955.23   $955.20   $955.20