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	$37.68	6.300%	$40.0538	$40.05	$40.05	$40.10
Purchase #2	$198.27	5.568%	$209.3097	$209.31	$209.30	$209.30
Purchase #3	$89.70	12.232%	$100.6721	$100.67	$100.65	$100.70
Purchase #4	$138.95	5.464%	$146.5422	$146.54	$146.55	$146.50
Purchase #5	$159.59	5.777%	$168.8095	$168.81	$168.80	$168.80
Purchase #6	$234.51	4.108%	$244.1437	$244.14	$244.15	$244.10
Purchase #7	$217.55	7.612%	$234.1099	$234.11	$234.10	$234.10
7 purchase totals =	$1,076.25		$1,143.6409	$1,143.63	$1,143.60	$1,143.60