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	$40.60	3.701%	$42.1026	$42.10	$42.10	$42.10
Purchase #2	$194.27	12.557%	$218.6645	$218.66	$218.65	$218.70
Purchase #3	$237.64	4.218%	$247.6637	$247.66	$247.65	$247.70
Purchase #4	$102.77	3.544%	$106.4122	$106.41	$106.40	$106.40
Purchase #5	$78.81	3.296%	$81.4076	$81.41	$81.40	$81.40
Purchase #6	$250.78	8.658%	$272.4925	$272.49	$272.50	$272.50
Purchase #7	$78.35	9.505%	$85.7972	$85.80	$85.80	$85.80
7 purchase totals =	$983.22		$1,054.5403	$1,054.53	$1,054.50	$1,054.60