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 $248.37   8.187%   $268.7041   $268.70   $268.70   $268.70  
  Purchase #2 $151.42   9.863%   $166.3546   $166.35   $166.35   $166.40  
  Purchase #3 $77.59   7.636%   $83.5148   $83.51   $83.50   $83.50  
  Purchase #4 $39.35   3.663%   $40.7914   $40.79   $40.80   $40.80  
  Purchase #5 $218.40   8.451%   $236.857   $236.86   $236.85   $236.90  
  Purchase #6 $229.51   13.702%   $260.9575   $260.96   $260.95   $261.00  
  Purchase #7 $54.34   4.457%   $56.7619   $56.76   $56.75   $56.80  
  7 purchase totals = $1,018.98       $1,113.9413   $1,113.93   $1,113.90   $1,114.10