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	$65.34	13.449%	$74.1276	$74.13	$74.15	$74.10
Purchase #2	$189.75	3.331%	$196.0706	$196.07	$196.05	$196.10
Purchase #3	$139.79	3.362%	$144.4897	$144.49	$144.50	$144.50
Purchase #4	$187.71	10.551%	$207.5153	$207.52	$207.50	$207.50
Purchase #5	$38.77	7.680%	$41.7475	$41.75	$41.75	$41.70
Purchase #6	$36.27	6.334%	$38.5673	$38.57	$38.55	$38.60
Purchase #7	$115.74	13.470%	$131.3302	$131.33	$131.35	$131.30
7 purchase totals =	$773.37		$833.8482	$833.86	$833.85	$833.80