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	$14.92	12.536%	$16.7904	$16.79	$16.80	$16.80
Purchase #2	$55.58	7.250%	$59.6096	$59.61	$59.60	$59.60
Purchase #3	$95.90	5.142%	$100.8312	$100.83	$100.85	$100.80
Purchase #4	$120.46	13.294%	$136.474	$136.47	$136.45	$136.50
Purchase #5	$64.50	11.350%	$71.8208	$71.82	$71.80	$71.80
Purchase #6	$47.30	4.496%	$49.4266	$49.43	$49.45	$49.40
Purchase #7	$193.40	10.543%	$213.7902	$213.79	$213.80	$213.80
7 purchase totals =	$592.06		$648.7428	$648.74	$648.75	$648.70