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	$5.89	4.452%	$6.1522	$6.15	$6.15	$6.20
Purchase #2	$177.73	7.808%	$191.6072	$191.61	$191.60	$191.60
Purchase #3	$36.54	13.285%	$41.3943	$41.39	$41.40	$41.40
Purchase #4	$56.51	5.167%	$59.4299	$59.43	$59.45	$59.40
Purchase #5	$103.74	10.375%	$114.503	$114.50	$114.50	$114.50
Purchase #6	$134.61	3.480%	$139.2944	$139.29	$139.30	$139.30
Purchase #7	$179.65	6.566%	$191.4458	$191.45	$191.45	$191.40
7 purchase totals =	$694.67		$743.8268	$743.82	$743.85	$743.80