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	$165.67	11.249%	$184.3062	$184.31	$184.30	$184.30
Purchase #2	$96.30	4.690%	$100.8165	$100.82	$100.80	$100.80
Purchase #3	$67.50	10.785%	$74.7799	$74.78	$74.80	$74.80
Purchase #4	$51.25	4.448%	$53.5296	$53.53	$53.55	$53.50
Purchase #5	$89.37	12.610%	$100.6396	$100.64	$100.65	$100.60
Purchase #6	$234.29	10.688%	$259.3309	$259.33	$259.35	$259.30
Purchase #7	$194.50	9.375%	$212.7344	$212.73	$212.75	$212.70
7 purchase totals =	$898.88		$986.1371	$986.14	$986.20	$986.00