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 $243.57   10.401%   $268.9037   $268.90   $268.90   $268.90  
  Purchase #2 $233.55   12.823%   $263.4981   $263.50   $263.50   $263.50  
  Purchase #3 $152.59   12.410%   $171.5264   $171.53   $171.55   $171.50  
  Purchase #4 $16.28   8.190%   $17.6133   $17.61   $17.60   $17.60  
  Purchase #5 $246.79   3.514%   $255.4622   $255.46   $255.45   $255.50  
  Purchase #6 $64.96   4.306%   $67.7572   $67.76   $67.75   $67.80  
  Purchase #7 $181.96   7.267%   $195.183   $195.18   $195.20   $195.20  
  7 purchase totals = $1,139.70       $1,239.9439   $1,239.94   $1,239.95   $1,240.00