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 $243.83   7.776%   $262.7902   $262.79   $262.80   $262.80  
  Purchase #2 $141.42   5.133%   $148.6791   $148.68   $148.70   $148.70  
  Purchase #3 $153.49   5.527%   $161.9734   $161.97   $161.95   $162.00  
  Purchase #4 $165.94   3.567%   $171.8591   $171.86   $171.85   $171.90  
  Purchase #5 $249.80   11.453%   $278.4096   $278.41   $278.40   $278.40  
  Purchase #6 $248.30   10.578%   $274.5652   $274.57   $274.55   $274.60  
  Purchase #7 $108.28   3.563%   $112.138   $112.14   $112.15   $112.10  
  7 purchase totals = $1,311.06       $1,410.4146   $1,410.42   $1,410.40   $1,410.50