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	$191.35	6.680%	$204.1322	$204.13	$204.15	$204.10
Purchase #2	$142.72	6.189%	$151.5529	$151.55	$151.55	$151.60
Purchase #3	$239.26	13.171%	$270.7729	$270.77	$270.75	$270.80
Purchase #4	$206.54	5.484%	$217.8667	$217.87	$217.85	$217.90
Purchase #5	$159.87	3.388%	$165.2864	$165.29	$165.30	$165.30
Purchase #6	$166.48	8.130%	$180.0148	$180.01	$180.00	$180.00
Purchase #7	$84.99	6.733%	$90.7124	$90.71	$90.70	$90.70
7 purchase totals =	$1,191.21		$1,280.3383	$1,280.33	$1,280.30	$1,280.40