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	$81.93	10.416%	$90.4638	$90.46	$90.45	$90.50
Purchase #2	$227.70	8.857%	$247.8674	$247.87	$247.85	$247.90
Purchase #3	$155.82	11.355%	$173.5134	$173.51	$173.50	$173.50
Purchase #4	$64.34	4.560%	$67.2739	$67.27	$67.25	$67.30
Purchase #5	$241.31	5.277%	$254.0439	$254.04	$254.05	$254.00
Purchase #6	$77.73	10.509%	$85.8986	$85.90	$85.90	$85.90
Purchase #7	$200.65	4.563%	$209.8057	$209.81	$209.80	$209.80
7 purchase totals =	$1,049.48		$1,128.8667	$1,128.86	$1,128.80	$1,128.90