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 $248.63   7.224%   $266.591   $266.59   $266.60   $266.60  
  Purchase #2 $173.68   11.415%   $193.5056   $193.51   $193.50   $193.50  
  Purchase #3 $40.61   8.685%   $44.137   $44.14   $44.15   $44.10  
  Purchase #4 $104.67   11.664%   $116.8787   $116.88   $116.90   $116.90  
  Purchase #5 $203.27   13.749%   $231.2176   $231.22   $231.20   $231.20  
  Purchase #6 $236.70   3.262%   $244.4212   $244.42   $244.40   $244.40  
  Purchase #7 $132.29   11.762%   $147.8499   $147.85   $147.85   $147.80  
  7 purchase totals = $1,139.85       $1,244.6010   $1,244.61   $1,244.60   $1,244.50