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	$42.40	5.187%	$44.5993	$44.60	$44.60	$44.60
Purchase #2	$24.68	12.846%	$27.8504	$27.85	$27.85	$27.90
Purchase #3	$18.38	4.670%	$19.2383	$19.24	$19.25	$19.20
Purchase #4	$34.94	7.753%	$37.6489	$37.65	$37.65	$37.60
Purchase #5	$130.92	10.349%	$144.4689	$144.47	$144.45	$144.50
Purchase #6	$41.83	9.557%	$45.8277	$45.83	$45.85	$45.80
Purchase #7	$116.39	12.302%	$130.7083	$130.71	$130.70	$130.70
7 purchase totals =	$409.54		$450.3418	$450.35	$450.35	$450.30