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 $61.73   10.672%   $68.3178   $68.32   $68.30   $68.30  
  Purchase #2 $241.28   7.221%   $258.7028   $258.70   $258.70   $258.70  
  Purchase #3 $80.27   4.174%   $83.6205   $83.62   $83.60   $83.60  
  Purchase #4 $225.58   12.114%   $252.9068   $252.91   $252.90   $252.90  
  Purchase #5 $220.97   12.622%   $248.8608   $248.86   $248.85   $248.90  
  Purchase #6 $10.63   13.283%   $12.042   $12.04   $12.05   $12.00  
  Purchase #7 $229.30   13.272%   $259.7327   $259.73   $259.75   $259.70  
  7 purchase totals = $1,069.76       $1,184.1834   $1,184.18   $1,184.15   $1,184.10