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	$124.78	5.401%	$131.5194	$131.52	$131.50	$131.50
Purchase #2	$226.30	6.728%	$241.5255	$241.53	$241.55	$241.50
Purchase #3	$247.49	7.454%	$265.9379	$265.94	$265.95	$265.90
Purchase #4	$227.28	11.383%	$253.1513	$253.15	$253.15	$253.20
Purchase #5	$207.89	7.671%	$223.8372	$223.84	$223.85	$223.80
Purchase #6	$128.42	12.786%	$144.8398	$144.84	$144.85	$144.80
Purchase #7	$83.66	6.230%	$88.872	$88.87	$88.85	$88.90
7 purchase totals =	$1,245.82		$1,349.6831	$1,349.69	$1,349.70	$1,349.60