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 $215.99   11.554%   $240.9455   $240.95   $240.95   $240.90  
  Purchase #2 $210.26   7.660%   $226.3659   $226.37   $226.35   $226.40  
  Purchase #3 $31.40   11.677%   $35.0666   $35.07   $35.05   $35.10  
  Purchase #4 $58.29   3.369%   $60.2538   $60.25   $60.25   $60.30  
  Purchase #5 $45.25   12.446%   $50.8818   $50.88   $50.90   $50.90  
  Purchase #6 $245.96   5.396%   $259.232   $259.23   $259.25   $259.20  
  Purchase #7 $132.88   11.565%   $148.2476   $148.25   $148.25   $148.20  
  7 purchase totals = $940.03       $1,020.9932   $1,021.00   $1,021.00   $1,021.00