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 $95.63   12.189%   $107.2863   $107.29   $107.30   $107.30  
  Purchase #2 $131.59   10.795%   $145.7951   $145.80   $145.80   $145.80  
  Purchase #3 $15.82   7.514%   $17.0087   $17.01   $17.00   $17.00  
  Purchase #4 $206.63   3.103%   $213.0417   $213.04   $213.05   $213.00  
  Purchase #5 $53.62   4.555%   $56.0624   $56.06   $56.05   $56.10  
  Purchase #6 $61.27   10.671%   $67.8081   $67.81   $67.80   $67.80  
  Purchase #7 $89.28   12.622%   $100.5489   $100.55   $100.55   $100.50  
  7 purchase totals = $653.84       $707.5512   $707.56   $707.55   $707.50