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	$84.28	8.266%	$91.2466	$91.25	$91.25	$91.20
Purchase #2	$44.82	5.305%	$47.1977	$47.20	$47.20	$47.20
Purchase #3	$155.54	12.863%	$175.5471	$175.55	$175.55	$175.50
Purchase #4	$103.40	6.243%	$109.8553	$109.86	$109.85	$109.90
Purchase #5	$80.55	6.350%	$85.6649	$85.66	$85.65	$85.70
Purchase #6	$61.75	4.523%	$64.543	$64.54	$64.55	$64.50
Purchase #7	$34.45	13.510%	$39.1042	$39.10	$39.10	$39.10
7 purchase totals =	$564.79		$613.1588	$613.16	$613.15	$613.10