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	$86.28	3.425%	$89.2351	$89.24	$89.25	$89.20
Purchase #2	$178.74	12.164%	$200.4819	$200.48	$200.50	$200.50
Purchase #3	$169.92	3.730%	$176.258	$176.26	$176.25	$176.30
Purchase #4	$59.51	11.798%	$66.531	$66.53	$66.55	$66.50
Purchase #5	$100.95	9.245%	$110.2828	$110.28	$110.30	$110.30
Purchase #6	$94.68	10.551%	$104.6697	$104.67	$104.65	$104.70
Purchase #7	$173.44	9.870%	$190.5585	$190.56	$190.55	$190.60
7 purchase totals =	$863.52		$938.0170	$938.02	$938.05	$938.10