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	$138.70	7.755%	$149.4562	$149.46	$149.45	$149.50
Purchase #2	$164.47	9.205%	$179.6095	$179.61	$179.60	$179.60
Purchase #3	$182.33	7.607%	$196.1998	$196.20	$196.20	$196.20
Purchase #4	$30.27	4.420%	$31.6079	$31.61	$31.60	$31.60
Purchase #5	$35.29	10.196%	$38.8882	$38.89	$38.90	$38.90
Purchase #6	$88.72	6.472%	$94.462	$94.46	$94.45	$94.50
Purchase #7	$138.69	5.313%	$146.0586	$146.06	$146.05	$146.10
7 purchase totals =	$778.47		$836.2822	$836.29	$836.25	$836.40