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	$26.59	5.537%	$28.0623	$28.06	$28.05	$28.10
Purchase #2	$145.77	4.582%	$152.4492	$152.45	$152.45	$152.40
Purchase #3	$191.91	7.602%	$206.499	$206.50	$206.50	$206.50
Purchase #4	$97.65	12.575%	$109.9295	$109.93	$109.95	$109.90
Purchase #5	$144.98	4.496%	$151.4983	$151.50	$151.50	$151.50
Purchase #6	$69.32	13.288%	$78.5312	$78.53	$78.55	$78.50
Purchase #7	$107.74	4.552%	$112.6443	$112.64	$112.65	$112.60
7 purchase totals =	$783.96		$839.6138	$839.61	$839.65	$839.50