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	$69.37	13.592%	$78.7988	$78.80	$78.80	$78.80
Purchase #2	$144.49	10.336%	$159.4245	$159.42	$159.40	$159.40
Purchase #3	$122.98	10.809%	$136.2729	$136.27	$136.25	$136.30
Purchase #4	$94.34	10.679%	$104.4146	$104.41	$104.40	$104.40
Purchase #5	$184.27	8.127%	$199.2456	$199.25	$199.25	$199.20
Purchase #6	$77.91	3.841%	$80.9025	$80.90	$80.90	$80.90
Purchase #7	$158.67	10.672%	$175.6033	$175.60	$175.60	$175.60
7 purchase totals =	$852.03		$934.6622	$934.65	$934.60	$934.60