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	$78.54	13.389%	$89.0557	$89.06	$89.05	$89.10
Purchase #2	$25.78	11.816%	$28.8262	$28.83	$28.85	$28.80
Purchase #3	$123.26	4.281%	$128.5368	$128.54	$128.55	$128.50
Purchase #4	$157.27	7.779%	$169.504	$169.50	$169.50	$169.50
Purchase #5	$188.63	4.845%	$197.7691	$197.77	$197.75	$197.80
Purchase #6	$38.71	5.225%	$40.7326	$40.73	$40.75	$40.70
Purchase #7	$51.69	10.494%	$57.1143	$57.11	$57.10	$57.10
7 purchase totals =	$663.88		$711.5387	$711.54	$711.55	$711.50