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	$18.95	7.216%	$20.3174	$20.32	$20.30	$20.30
Purchase #2	$37.29	7.415%	$40.0551	$40.06	$40.05	$40.10
Purchase #3	$28.58	4.191%	$29.7778	$29.78	$29.80	$29.80
Purchase #4	$194.29	7.210%	$208.2983	$208.30	$208.30	$208.30
Purchase #5	$142.74	4.804%	$149.5972	$149.60	$149.60	$149.60
Purchase #6	$112.95	5.106%	$118.7172	$118.72	$118.70	$118.70
Purchase #7	$95.84	3.715%	$99.4005	$99.40	$99.40	$99.40
7 purchase totals =	$630.64		$666.1635	$666.18	$666.15	$666.20