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 $238.80   5.648%   $252.2874   $252.29   $252.30   $252.30  
  Purchase #2 $128.30   9.494%   $140.4808   $140.48   $140.50   $140.50  
  Purchase #3 $11.48   8.485%   $12.4541   $12.45   $12.45   $12.50  
  Purchase #4 $80.75   7.238%   $86.5947   $86.59   $86.60   $86.60  
  Purchase #5 $221.84   6.712%   $236.7299   $236.73   $236.75   $236.70  
  Purchase #6 $229.82   5.173%   $241.7086   $241.71   $241.70   $241.70  
  Purchase #7 $56.31   8.169%   $60.91   $60.91   $60.90   $60.90  
  7 purchase totals = $967.30       $1,031.1655   $1,031.16   $1,031.20   $1,031.20