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	$244.91	13.216%	$277.2773	$277.28	$277.30	$277.30
Purchase #2	$36.43	10.452%	$40.2377	$40.24	$40.25	$40.20
Purchase #3	$131.66	10.424%	$145.3842	$145.38	$145.40	$145.40
Purchase #4	$141.25	7.190%	$151.4059	$151.41	$151.40	$151.40
Purchase #5	$37.69	13.400%	$42.7405	$42.74	$42.75	$42.70
Purchase #6	$185.44	10.451%	$204.8203	$204.82	$204.80	$204.80
Purchase #7	$152.77	10.388%	$168.6397	$168.64	$168.65	$168.60
7 purchase totals =	$930.15		$1,030.5056	$1,030.51	$1,030.55	$1,030.40