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 $172.87   12.544%   $194.5548   $194.55   $194.55   $194.60  
  Purchase #2 $22.40   5.694%   $23.6755   $23.68   $23.70   $23.70  
  Purchase #3 $60.91   9.465%   $66.6751   $66.68   $66.70   $66.70  
  Purchase #4 $123.55   6.179%   $131.1842   $131.18   $131.20   $131.20  
  Purchase #5 $98.36   7.579%   $105.8147   $105.81   $105.80   $105.80  
  Purchase #6 $198.35   5.277%   $208.8169   $208.82   $208.80   $208.80  
  Purchase #7 $95.84   7.480%   $103.0088   $103.01   $103.00   $103.00  
  7 purchase totals = $772.28       $833.7300   $833.73   $833.75   $833.80