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	$13.46	13.747%	$15.3103	$15.31	$15.30	$15.30
Purchase #2	$63.90	3.318%	$66.0202	$66.02	$66.00	$66.00
Purchase #3	$49.39	8.563%	$53.6193	$53.62	$53.60	$53.60
Purchase #4	$77.66	3.796%	$80.608	$80.61	$80.60	$80.60
Purchase #5	$105.32	4.169%	$109.7108	$109.71	$109.70	$109.70
Purchase #6	$84.46	6.777%	$90.1839	$90.18	$90.20	$90.20
Purchase #7	$91.96	7.426%	$98.7889	$98.79	$98.80	$98.80
7 purchase totals =	$486.15		$514.2414	$514.24	$514.20	$514.20