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	$149.45	10.727%	$165.4815	$165.48	$165.50	$165.50
Purchase #2	$81.87	7.266%	$87.8187	$87.82	$87.80	$87.80
Purchase #3	$54.77	12.137%	$61.4174	$61.42	$61.40	$61.40
Purchase #4	$46.59	13.505%	$52.882	$52.88	$52.90	$52.90
Purchase #5	$223.50	8.305%	$242.0617	$242.06	$242.05	$242.10
Purchase #6	$184.35	11.817%	$206.1346	$206.13	$206.15	$206.10
Purchase #7	$247.83	9.366%	$271.0418	$271.04	$271.05	$271.00
7 purchase totals =	$988.36		$1,086.8377	$1,086.83	$1,086.85	$1,086.80