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	$140.53	8.739%	$152.8109	$152.81	$152.80	$152.80
Purchase #2	$64.58	4.147%	$67.2581	$67.26	$67.25	$67.30
Purchase #3	$111.39	8.173%	$120.4939	$120.49	$120.50	$120.50
Purchase #4	$156.63	7.700%	$168.6905	$168.69	$168.70	$168.70
Purchase #5	$57.89	6.313%	$61.5446	$61.54	$61.55	$61.50
Purchase #6	$214.50	7.744%	$231.1109	$231.11	$231.10	$231.10
Purchase #7	$249.75	6.826%	$266.7979	$266.80	$266.80	$266.80
7 purchase totals =	$995.27		$1,068.7068	$1,068.70	$1,068.70	$1,068.70