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 $241.54   9.173%   $263.6965   $263.70   $263.70   $263.70  
  Purchase #2 $151.62   8.838%   $165.0202   $165.02   $165.00   $165.00  
  Purchase #3 $93.84   4.141%   $97.7259   $97.73   $97.75   $97.70  
  Purchase #4 $82.37   10.452%   $90.9793   $90.98   $91.00   $91.00  
  Purchase #5 $105.37   12.756%   $118.811   $118.81   $118.80   $118.80  
  Purchase #6 $92.89   4.242%   $96.8304   $96.83   $96.85   $96.80  
  Purchase #7 $237.86   4.436%   $248.4115   $248.41   $248.40   $248.40  
  7 purchase totals = $1,005.49       $1,081.4748   $1,081.48   $1,081.50   $1,081.40