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	$151.71	4.373%	$158.3443	$158.34	$158.35	$158.30
Purchase #2	$174.91	8.764%	$190.2391	$190.24	$190.25	$190.20
Purchase #3	$62.46	8.494%	$67.7654	$67.77	$67.75	$67.80
Purchase #4	$91.53	13.866%	$104.2215	$104.22	$104.20	$104.20
Purchase #5	$62.37	7.813%	$67.243	$67.24	$67.25	$67.20
Purchase #6	$144.62	4.140%	$150.6073	$150.61	$150.60	$150.60
Purchase #7	$132.66	6.780%	$141.6543	$141.65	$141.65	$141.70
7 purchase totals =	$820.26		$880.0749	$880.07	$880.05	$880.00