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	$78.81	13.367%	$89.3445	$89.34	$89.35	$89.30
Purchase #2	$184.31	7.513%	$198.1572	$198.16	$198.15	$198.20
Purchase #3	$17.90	11.419%	$19.944	$19.94	$19.95	$19.90
Purchase #4	$33.79	4.402%	$35.2774	$35.28	$35.30	$35.30
Purchase #5	$16.78	5.828%	$17.7579	$17.76	$17.75	$17.80
Purchase #6	$61.52	7.644%	$66.2226	$66.22	$66.20	$66.20
Purchase #7	$130.43	3.628%	$135.162	$135.16	$135.15	$135.20
7 purchase totals =	$523.54		$561.8656	$561.86	$561.85	$561.90