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	$69.50	6.826%	$74.2441	$74.24	$74.25	$74.20
Purchase #2	$169.33	13.180%	$191.6477	$191.65	$191.65	$191.60
Purchase #3	$83.71	8.805%	$91.0807	$91.08	$91.10	$91.10
Purchase #4	$164.92	4.721%	$172.7059	$172.71	$172.70	$172.70
Purchase #5	$28.53	10.272%	$31.4606	$31.46	$31.45	$31.50
Purchase #6	$164.51	7.557%	$176.942	$176.94	$176.95	$176.90
Purchase #7	$135.50	12.569%	$152.531	$152.53	$152.55	$152.50
7 purchase totals =	$816.00		$890.6120	$890.61	$890.65	$890.50