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 $246.64   5.503%   $260.2126   $260.21   $260.20   $260.20  
  Purchase #2 $235.53   7.120%   $252.2997   $252.30   $252.30   $252.30  
  Purchase #3 $146.70   11.339%   $163.3343   $163.33   $163.35   $163.30  
  Purchase #4 $149.27   5.477%   $157.4455   $157.45   $157.45   $157.40  
  Purchase #5 $100.63   4.662%   $105.3214   $105.32   $105.30   $105.30  
  Purchase #6 $213.66   13.704%   $242.94   $242.94   $242.95   $242.90  
  Purchase #7 $33.37   8.231%   $36.1167   $36.12   $36.10   $36.10  
  7 purchase totals = $1,125.80       $1,217.6702   $1,217.67   $1,217.65   $1,217.50