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	$175.65	8.149%	$189.9637	$189.96	$189.95	$190.00
Purchase #2	$165.45	4.529%	$172.9432	$172.94	$172.95	$172.90
Purchase #3	$24.97	13.656%	$28.3799	$28.38	$28.40	$28.40
Purchase #4	$137.55	3.209%	$141.964	$141.96	$141.95	$142.00
Purchase #5	$113.62	13.292%	$128.7224	$128.72	$128.70	$128.70
Purchase #6	$132.37	7.344%	$142.0913	$142.09	$142.10	$142.10
Purchase #7	$32.99	13.573%	$37.4677	$37.47	$37.45	$37.50
7 purchase totals =	$782.60		$841.5322	$841.52	$841.50	$841.60