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	$126.38	10.308%	$139.4073	$139.41	$139.40	$139.40
Purchase #2	$178.64	6.321%	$189.9318	$189.93	$189.95	$189.90
Purchase #3	$58.85	10.722%	$65.1599	$65.16	$65.15	$65.20
Purchase #4	$54.49	12.264%	$61.1727	$61.17	$61.15	$61.20
Purchase #5	$190.35	5.104%	$200.0655	$200.07	$200.05	$200.10
Purchase #6	$31.68	5.190%	$33.3242	$33.32	$33.30	$33.30
Purchase #7	$14.61	8.851%	$15.9031	$15.90	$15.90	$15.90
7 purchase totals =	$655.00		$704.9645	$704.96	$704.90	$705.00