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	$165.49	8.624%	$179.7619	$179.76	$179.75	$179.80
Purchase #2	$153.83	7.535%	$165.4211	$165.42	$165.40	$165.40
Purchase #3	$188.78	5.674%	$199.4914	$199.49	$199.50	$199.50
Purchase #4	$213.32	7.296%	$228.8838	$228.88	$228.90	$228.90
Purchase #5	$204.32	7.127%	$218.8819	$218.88	$218.90	$218.90
Purchase #6	$147.63	7.601%	$158.8514	$158.85	$158.85	$158.90
Purchase #7	$232.88	9.471%	$254.9361	$254.94	$254.95	$254.90
7 purchase totals =	$1,306.25		$1,406.2276	$1,406.22	$1,406.25	$1,406.30