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	$110.29	4.142%	$114.8582	$114.86	$114.85	$114.90
Purchase #2	$145.81	13.331%	$165.2479	$165.25	$165.25	$165.20
Purchase #3	$57.66	5.409%	$60.7788	$60.78	$60.80	$60.80
Purchase #4	$44.87	12.446%	$50.4545	$50.45	$50.45	$50.50
Purchase #5	$131.52	12.162%	$147.5155	$147.52	$147.50	$147.50
Purchase #6	$8.27	3.235%	$8.5375	$8.54	$8.55	$8.50
Purchase #7	$39.67	8.451%	$43.0225	$43.02	$43.00	$43.00
7 purchase totals =	$538.09		$590.4149	$590.42	$590.40	$590.40