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	$38.70	8.793%	$42.1029	$42.10	$42.10	$42.10
Purchase #2	$152.32	13.849%	$173.4148	$173.41	$173.40	$173.40
Purchase #3	$203.27	11.691%	$227.0343	$227.03	$227.05	$227.00
Purchase #4	$129.86	12.641%	$146.2756	$146.28	$146.30	$146.30
Purchase #5	$141.72	7.111%	$151.7977	$151.80	$151.80	$151.80
Purchase #6	$206.53	8.308%	$223.6885	$223.69	$223.70	$223.70
Purchase #7	$118.78	9.643%	$130.234	$130.23	$130.25	$130.20
7 purchase totals =	$991.18		$1,094.5478	$1,094.54	$1,094.60	$1,094.50