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	$74.61	6.488%	$79.4507	$79.45	$79.45	$79.50
Purchase #2	$223.45	3.586%	$231.4629	$231.46	$231.45	$231.50
Purchase #3	$239.80	8.689%	$260.6362	$260.64	$260.65	$260.60
Purchase #4	$45.27	12.470%	$50.9152	$50.92	$50.90	$50.90
Purchase #5	$57.45	6.369%	$61.109	$61.11	$61.10	$61.10
Purchase #6	$109.61	8.519%	$118.9477	$118.95	$118.95	$118.90
Purchase #7	$86.33	3.491%	$89.3438	$89.34	$89.35	$89.30
7 purchase totals =	$836.52		$891.8655	$891.87	$891.85	$891.80