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	$222.35	8.624%	$241.5255	$241.53	$241.55	$241.50
Purchase #2	$170.74	11.784%	$190.86	$190.86	$190.85	$190.90
Purchase #3	$133.28	6.184%	$141.522	$141.52	$141.50	$141.50
Purchase #4	$129.59	8.526%	$140.6388	$140.64	$140.65	$140.60
Purchase #5	$35.74	3.628%	$37.0366	$37.04	$37.05	$37.00
Purchase #6	$234.56	7.548%	$252.2646	$252.26	$252.25	$252.30
Purchase #7	$87.50	10.618%	$96.7908	$96.79	$96.80	$96.80
7 purchase totals =	$1,013.76		$1,100.6383	$1,100.64	$1,100.65	$1,100.60