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	$72.98	11.171%	$81.1326	$81.13	$81.15	$81.10
Purchase #2	$108.35	5.491%	$114.2995	$114.30	$114.30	$114.30
Purchase #3	$103.51	5.792%	$109.5053	$109.51	$109.50	$109.50
Purchase #4	$179.50	3.572%	$185.9117	$185.91	$185.90	$185.90
Purchase #5	$87.68	13.674%	$99.6694	$99.67	$99.65	$99.70
Purchase #6	$165.40	8.700%	$179.7898	$179.79	$179.80	$179.80
Purchase #7	$67.93	13.766%	$77.2812	$77.28	$77.30	$77.30
7 purchase totals =	$785.35		$847.5895	$847.59	$847.60	$847.60