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	$100.73	4.451%	$105.2135	$105.21	$105.20	$105.20
Purchase #2	$215.84	4.543%	$225.6456	$225.65	$225.65	$225.60
Purchase #3	$45.37	10.271%	$50.03	$50.03	$50.05	$50.00
Purchase #4	$199.35	12.228%	$223.7265	$223.73	$223.75	$223.70
Purchase #5	$196.33	7.610%	$211.2707	$211.27	$211.25	$211.30
Purchase #6	$132.73	10.482%	$146.6428	$146.64	$146.65	$146.60
Purchase #7	$164.64	9.664%	$180.5508	$180.55	$180.55	$180.60
7 purchase totals =	$1,054.99		$1,143.0799	$1,143.08	$1,143.10	$1,143.00