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 $59.71   4.670%   $62.4985   $62.50   $62.50   $62.50  
  Purchase #2 $248.70   12.506%   $279.8024   $279.80   $279.80   $279.80  
  Purchase #3 $114.93   3.853%   $119.3583   $119.36   $119.35   $119.40  
  Purchase #4 $53.66   12.751%   $60.5022   $60.50   $60.50   $60.50  
  Purchase #5 $214.88   3.801%   $223.0476   $223.05   $223.05   $223.00  
  Purchase #6 $234.83   9.229%   $256.5025   $256.50   $256.50   $256.50  
  Purchase #7 $227.63   5.843%   $240.9304   $240.93   $240.95   $240.90  
  7 purchase totals = $1,154.34       $1,242.6419   $1,242.64   $1,242.65   $1,242.60