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 $236.73   11.625%   $264.2499   $264.25   $264.25   $264.20  
  Purchase #2 $136.93   5.284%   $144.1654   $144.17   $144.15   $144.20  
  Purchase #3 $190.32   8.607%   $206.7008   $206.70   $206.70   $206.70  
  Purchase #4 $69.63   6.125%   $73.8948   $73.89   $73.90   $73.90  
  Purchase #5 $79.57   3.219%   $82.1314   $82.13   $82.15   $82.10  
  Purchase #6 $83.53   5.690%   $88.2829   $88.28   $88.30   $88.30  
  Purchase #7 $183.25   3.109%   $188.9472   $188.95   $188.95   $188.90  
  7 purchase totals = $979.96       $1,048.3724   $1,048.37   $1,048.40   $1,048.30