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 $55.64   9.190%   $60.7533   $60.75   $60.75   $60.80  
  Purchase #2 $31.57   12.455%   $35.502   $35.50   $35.50   $35.50  
  Purchase #3 $52.64   6.207%   $55.9074   $55.91   $55.90   $55.90  
  Purchase #4 $127.31   4.794%   $133.4132   $133.41   $133.40   $133.40  
  Purchase #5 $248.66   10.122%   $273.8294   $273.83   $273.85   $273.80  
  Purchase #6 $120.86   9.349%   $132.1592   $132.16   $132.15   $132.20  
  Purchase #7 $67.40   6.573%   $71.8302   $71.83   $71.85   $71.80  
  7 purchase totals = $704.08       $763.3947   $763.39   $763.40   $763.40