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 $61.72   12.121%   $69.2011   $69.20   $69.20   $69.20  
  Purchase #2 $229.63   8.762%   $249.7502   $249.75   $249.75   $249.80  
  Purchase #3 $248.32   7.243%   $266.3058   $266.31   $266.30   $266.30  
  Purchase #4 $83.40   11.402%   $92.9093   $92.91   $92.90   $92.90  
  Purchase #5 $157.57   13.428%   $178.7285   $178.73   $178.75   $178.70  
  Purchase #6 $17.33   12.796%   $19.5475   $19.55   $19.55   $19.50  
  Purchase #7 $212.72   4.690%   $222.6966   $222.70   $222.70   $222.70  
  7 purchase totals = $1,010.69       $1,099.1390   $1,099.15   $1,099.15   $1,099.10