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	$123.51	6.569%	$131.6234	$131.62	$131.60	$131.60
Purchase #2	$132.62	6.823%	$141.6687	$141.67	$141.65	$141.70
Purchase #3	$124.86	9.818%	$137.1188	$137.12	$137.10	$137.10
Purchase #4	$243.58	6.670%	$259.8268	$259.83	$259.85	$259.80
Purchase #5	$45.95	8.689%	$49.9426	$49.94	$49.95	$49.90
Purchase #6	$166.76	13.254%	$188.8624	$188.86	$188.85	$188.90
Purchase #7	$191.43	4.742%	$200.5076	$200.51	$200.50	$200.50
7 purchase totals =	$1,028.71		$1,109.5503	$1,109.55	$1,109.50	$1,109.50