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	$119.55	3.121%	$123.2812	$123.28	$123.30	$123.30
Purchase #2	$32.69	12.180%	$36.6716	$36.67	$36.65	$36.70
Purchase #3	$217.63	7.801%	$234.6073	$234.61	$234.60	$234.60
Purchase #4	$235.69	8.220%	$255.0637	$255.06	$255.05	$255.10
Purchase #5	$130.30	3.245%	$134.5282	$134.53	$134.55	$134.50
Purchase #6	$74.91	3.406%	$77.4614	$77.46	$77.45	$77.50
Purchase #7	$119.25	7.831%	$128.5885	$128.59	$128.60	$128.60
7 purchase totals =	$930.02		$990.2019	$990.20	$990.20	$990.30