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	$235.92	3.508%	$244.1961	$244.20	$244.20	$244.20
Purchase #2	$81.74	13.181%	$92.5141	$92.51	$92.50	$92.50
Purchase #3	$127.50	10.751%	$141.2075	$141.21	$141.20	$141.20
Purchase #4	$209.39	5.700%	$221.3252	$221.33	$221.35	$221.30
Purchase #5	$144.84	9.440%	$158.5129	$158.51	$158.50	$158.50
Purchase #6	$231.53	10.471%	$255.7735	$255.77	$255.75	$255.80
Purchase #7	$163.80	10.127%	$180.388	$180.39	$180.40	$180.40
7 purchase totals =	$1,194.72		$1,293.9173	$1,293.92	$1,293.90	$1,293.90