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	$34.45	12.407%	$38.7242	$38.72	$38.70	$38.70
Purchase #2	$88.68	12.624%	$99.875	$99.88	$99.90	$99.90
Purchase #3	$161.66	8.515%	$175.4253	$175.43	$175.45	$175.40
Purchase #4	$90.72	3.812%	$94.1782	$94.18	$94.20	$94.20
Purchase #5	$54.73	5.807%	$57.9082	$57.91	$57.90	$57.90
Purchase #6	$31.41	5.494%	$33.1357	$33.14	$33.15	$33.10
Purchase #7	$127.79	8.230%	$138.3071	$138.31	$138.30	$138.30
7 purchase totals =	$589.44		$637.5537	$637.57	$637.60	$637.50