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	$120.32	11.298%	$133.9138	$133.91	$133.90	$133.90
Purchase #2	$42.69	4.802%	$44.74	$44.74	$44.75	$44.70
Purchase #3	$207.89	11.272%	$231.3234	$231.32	$231.30	$231.30
Purchase #4	$38.38	10.194%	$42.2925	$42.29	$42.30	$42.30
Purchase #5	$10.94	5.468%	$11.5382	$11.54	$11.55	$11.50
Purchase #6	$242.75	5.585%	$256.3076	$256.31	$256.30	$256.30
Purchase #7	$67.85	7.225%	$72.7522	$72.75	$72.75	$72.80
7 purchase totals =	$730.82		$792.8677	$792.86	$792.85	$792.80