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	$6.78	8.551%	$7.3598	$7.36	$7.35	$7.40
Purchase #2	$40.52	12.848%	$45.726	$45.73	$45.75	$45.70
Purchase #3	$103.60	7.597%	$111.4705	$111.47	$111.45	$111.50
Purchase #4	$26.45	4.158%	$27.5498	$27.55	$27.55	$27.50
Purchase #5	$231.91	4.380%	$242.0677	$242.07	$242.05	$242.10
Purchase #6	$218.77	13.829%	$249.0237	$249.02	$249.00	$249.00
Purchase #7	$147.36	12.201%	$165.3394	$165.34	$165.35	$165.30
7 purchase totals =	$775.39		$848.5369	$848.54	$848.50	$848.50