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	$50.91	8.651%	$55.3142	$55.31	$55.30	$55.30
Purchase #2	$189.33	3.615%	$196.1743	$196.17	$196.15	$196.20
Purchase #3	$239.86	5.176%	$252.2752	$252.28	$252.30	$252.30
Purchase #4	$54.73	5.184%	$57.5672	$57.57	$57.55	$57.60
Purchase #5	$56.79	8.827%	$61.8029	$61.80	$61.80	$61.80
Purchase #6	$76.73	12.673%	$86.454	$86.45	$86.45	$86.50
Purchase #7	$114.55	8.729%	$124.5491	$124.55	$124.55	$124.50
7 purchase totals =	$782.90		$834.1369	$834.13	$834.10	$834.20