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 $227.33   9.222%   $248.2944   $248.29   $248.30   $248.30  
  Purchase #2 $119.25   3.646%   $123.5979   $123.60   $123.60   $123.60  
  Purchase #3 $130.50   5.481%   $137.6527   $137.65   $137.65   $137.70  
  Purchase #4 $35.79   9.168%   $39.0712   $39.07   $39.05   $39.10  
  Purchase #5 $58.82   8.195%   $63.6403   $63.64   $63.65   $63.60  
  Purchase #6 $80.99   7.124%   $86.7597   $86.76   $86.75   $86.80  
  Purchase #7 $238.28   9.198%   $260.197   $260.20   $260.20   $260.20  
  7 purchase totals = $890.96       $959.2132   $959.21   $959.20   $959.30