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	$133.93	10.617%	$148.1493	$148.15	$148.15	$148.10
Purchase #2	$39.93	13.694%	$45.398	$45.40	$45.40	$45.40
Purchase #3	$148.65	6.674%	$158.5709	$158.57	$158.55	$158.60
Purchase #4	$12.85	12.789%	$14.4934	$14.49	$14.50	$14.50
Purchase #5	$74.33	8.772%	$80.8502	$80.85	$80.85	$80.90
Purchase #6	$25.73	6.238%	$27.335	$27.34	$27.35	$27.30
Purchase #7	$29.92	10.519%	$33.0673	$33.07	$33.05	$33.10
7 purchase totals =	$465.34		$507.8641	$507.87	$507.85	$507.90