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	$75.89	7.432%	$81.5301	$81.53	$81.55	$81.50
Purchase #2	$80.27	11.809%	$89.7491	$89.75	$89.75	$89.70
Purchase #3	$9.95	7.783%	$10.7244	$10.72	$10.70	$10.70
Purchase #4	$210.73	6.139%	$223.6667	$223.67	$223.65	$223.70
Purchase #5	$42.89	7.710%	$46.1968	$46.20	$46.20	$46.20
Purchase #6	$32.42	10.355%	$35.7771	$35.78	$35.80	$35.80
Purchase #7	$62.30	7.275%	$66.8323	$66.83	$66.85	$66.80
7 purchase totals =	$514.45		$554.4765	$554.48	$554.50	$554.40