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 $232.82   3.721%   $241.4832   $241.48   $241.50   $241.50  
  Purchase #2 $100.66   4.587%   $105.2773   $105.28   $105.30   $105.30  
  Purchase #3 $83.95   3.841%   $87.1745   $87.17   $87.15   $87.20  
  Purchase #4 $112.44   3.796%   $116.7082   $116.71   $116.70   $116.70  
  Purchase #5 $226.48   4.474%   $236.6127   $236.61   $236.60   $236.60  
  Purchase #6 $52.65   11.495%   $58.7021   $58.70   $58.70   $58.70  
  Purchase #7 $151.66   11.376%   $168.9128   $168.91   $168.90   $168.90  
  7 purchase totals = $960.66       $1,014.8708   $1,014.86   $1,014.85   $1,014.90