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 $248.26   8.368%   $269.0344   $269.03   $269.05   $269.00  
  Purchase #2 $108.36   7.716%   $116.7211   $116.72   $116.70   $116.70  
  Purchase #3 $172.99   7.592%   $186.1234   $186.12   $186.10   $186.10  
  Purchase #4 $73.27   7.521%   $78.7806   $78.78   $78.80   $78.80  
  Purchase #5 $203.64   10.432%   $224.8837   $224.88   $224.90   $224.90  
  Purchase #6 $186.35   13.387%   $211.2967   $211.30   $211.30   $211.30  
  Purchase #7 $197.96   9.504%   $216.7741   $216.77   $216.75   $216.80  
  7 purchase totals = $1,190.83       $1,303.6140   $1,303.60   $1,303.60   $1,303.60