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 $244.87   9.239%   $267.4935   $267.49   $267.50   $267.50  
  Purchase #2 $95.83   5.397%   $101.0019   $101.00   $101.00   $101.00  
  Purchase #3 $106.94   12.110%   $119.8904   $119.89   $119.90   $119.90  
  Purchase #4 $164.35   4.332%   $171.4696   $171.47   $171.45   $171.50  
  Purchase #5 $133.89   13.777%   $152.336   $152.34   $152.35   $152.30  
  Purchase #6 $166.79   11.470%   $185.9208   $185.92   $185.90   $185.90  
  Purchase #7 $185.28   8.825%   $201.631   $201.63   $201.65   $201.60  
  7 purchase totals = $1,097.95       $1,199.7432   $1,199.74   $1,199.75   $1,199.70