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 $70.64   7.597%   $76.0065   $76.01   $76.00   $76.00  
  Purchase #2 $33.63   9.800%   $36.9257   $36.93   $36.95   $36.90  
  Purchase #3 $212.83   7.856%   $229.5499   $229.55   $229.55   $229.50  
  Purchase #4 $231.38   9.781%   $254.0113   $254.01   $254.00   $254.00  
  Purchase #5 $66.74   8.313%   $72.2881   $72.29   $72.30   $72.30  
  Purchase #6 $115.62   6.684%   $123.348   $123.35   $123.35   $123.30  
  Purchase #7 $200.73   5.636%   $212.0431   $212.04   $212.05   $212.00  
  7 purchase totals = $931.57       $1,004.1726   $1,004.18   $1,004.20   $1,004.00