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 $69.31   6.328%   $73.6959   $73.70   $73.70   $73.70  
  Purchase #2 $187.67   3.302%   $193.8669   $193.87   $193.85   $193.90  
  Purchase #3 $53.85   5.417%   $56.7671   $56.77   $56.75   $56.80  
  Purchase #4 $56.63   6.572%   $60.3517   $60.35   $60.35   $60.40  
  Purchase #5 $13.34   11.523%   $14.8772   $14.88   $14.90   $14.90  
  Purchase #6 $159.58   5.478%   $168.3218   $168.32   $168.30   $168.30  
  Purchase #7 $83.81   13.274%   $94.9349   $94.93   $94.95   $94.90  
  7 purchase totals = $624.19       $662.8155   $662.82   $662.80   $662.90