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 $16.37   9.270%   $17.8875   $17.89   $17.90   $17.90  
  Purchase #2 $79.29   7.448%   $85.1955   $85.20   $85.20   $85.20  
  Purchase #3 $83.32   7.313%   $89.4132   $89.41   $89.40   $89.40  
  Purchase #4 $53.51   10.137%   $58.9343   $58.93   $58.95   $58.90  
  Purchase #5 $138.27   11.597%   $154.3052   $154.31   $154.30   $154.30  
  Purchase #6 $231.73   3.244%   $239.2473   $239.25   $239.25   $239.20  
  Purchase #7 $95.45   4.468%   $99.7147   $99.71   $99.70   $99.70  
  7 purchase totals = $697.94       $744.6977   $744.70   $744.70   $744.60