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	$145.58	3.449%	$150.6011	$150.60	$150.60	$150.60
Purchase #2	$250.49	9.146%	$273.3998	$273.40	$273.40	$273.40
Purchase #3	$198.58	12.726%	$223.8513	$223.85	$223.85	$223.90
Purchase #4	$151.89	13.803%	$172.8554	$172.86	$172.85	$172.90
Purchase #5	$144.41	6.356%	$153.5887	$153.59	$153.60	$153.60
Purchase #6	$144.81	9.496%	$158.5612	$158.56	$158.55	$158.60
Purchase #7	$93.88	9.549%	$102.8446	$102.84	$102.85	$102.80
7 purchase totals =	$1,129.64		$1,235.7021	$1,235.70	$1,235.70	$1,235.80