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	$14.40	4.780%	$15.0883	$15.09	$15.10	$15.10
Purchase #2	$175.65	5.585%	$185.4601	$185.46	$185.45	$185.50
Purchase #3	$80.37	11.249%	$89.4108	$89.41	$89.40	$89.40
Purchase #4	$203.91	10.369%	$225.0534	$225.05	$225.05	$225.10
Purchase #5	$209.58	6.777%	$223.7832	$223.78	$223.80	$223.80
Purchase #6	$33.72	5.862%	$35.6967	$35.70	$35.70	$35.70
Purchase #7	$17.54	6.717%	$18.7182	$18.72	$18.70	$18.70
7 purchase totals =	$735.17		$793.2107	$793.21	$793.20	$793.30