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	$15.89	13.870%	$18.0939	$18.09	$18.10	$18.10
Purchase #2	$113.70	8.230%	$123.0575	$123.06	$123.05	$123.10
Purchase #3	$200.66	9.449%	$219.6204	$219.62	$219.60	$219.60
Purchase #4	$70.54	11.767%	$78.8404	$78.84	$78.85	$78.80
Purchase #5	$184.90	3.644%	$191.6378	$191.64	$191.65	$191.60
Purchase #6	$69.31	3.501%	$71.7365	$71.74	$71.75	$71.70
Purchase #7	$180.27	5.260%	$189.7522	$189.75	$189.75	$189.80
7 purchase totals =	$835.27		$892.7387	$892.74	$892.75	$892.70