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	$106.78	4.409%	$111.4879	$111.49	$111.50	$111.50
Purchase #2	$233.62	7.316%	$250.7116	$250.71	$250.70	$250.70
Purchase #3	$131.41	5.367%	$138.4628	$138.46	$138.45	$138.50
Purchase #4	$145.82	5.673%	$154.0924	$154.09	$154.10	$154.10
Purchase #5	$85.61	3.530%	$88.632	$88.63	$88.65	$88.60
Purchase #6	$72.87	9.553%	$79.8313	$79.83	$79.85	$79.80
Purchase #7	$30.36	10.130%	$33.4355	$33.44	$33.45	$33.40
7 purchase totals =	$806.47		$856.6535	$856.65	$856.70	$856.60