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	$26.79	11.209%	$29.7929	$29.79	$29.80	$29.80
Purchase #2	$78.78	6.316%	$83.7557	$83.76	$83.75	$83.80
Purchase #3	$124.38	6.551%	$132.5281	$132.53	$132.55	$132.50
Purchase #4	$250.48	9.365%	$273.9375	$273.94	$273.95	$273.90
Purchase #5	$50.96	5.484%	$53.7546	$53.75	$53.75	$53.80
Purchase #6	$88.57	12.834%	$99.9371	$99.94	$99.95	$99.90
Purchase #7	$90.33	10.718%	$100.0116	$100.01	$100.00	$100.00
7 purchase totals =	$710.29		$773.7175	$773.72	$773.75	$773.70