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 $14.71   13.867%   $16.7498   $16.75   $16.75   $16.70  
  Purchase #2 $26.83   6.720%   $28.633   $28.63   $28.65   $28.60  
  Purchase #3 $70.80   5.486%   $74.6841   $74.68   $74.70   $74.70  
  Purchase #4 $224.69   7.404%   $241.326   $241.33   $241.35   $241.30  
  Purchase #5 $119.31   9.677%   $130.8556   $130.86   $130.85   $130.90  
  Purchase #6 $148.88   10.799%   $164.9576   $164.96   $164.95   $165.00  
  Purchase #7 $149.99   6.110%   $159.1544   $159.15   $159.15   $159.20  
  7 purchase totals = $755.21       $816.3605   $816.36   $816.40   $816.40