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 $17.34   12.767%   $19.5538   $19.55   $19.55   $19.60  
  Purchase #2 $223.25   8.700%   $242.6728   $242.67   $242.65   $242.70  
  Purchase #3 $66.73   3.137%   $68.8233   $68.82   $68.80   $68.80  
  Purchase #4 $115.36   3.260%   $119.1207   $119.12   $119.10   $119.10  
  Purchase #5 $195.80   7.253%   $210.0014   $210.00   $210.00   $210.00  
  Purchase #6 $44.65   12.532%   $50.2455   $50.25   $50.25   $50.20  
  Purchase #7 $196.28   9.350%   $214.6322   $214.63   $214.65   $214.60  
  7 purchase totals = $859.41       $925.0497   $925.04   $925.00   $925.00