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	$31.26	13.708%	$35.5451	$35.55	$35.55	$35.50
Purchase #2	$161.93	7.162%	$173.5274	$173.53	$173.55	$173.50
Purchase #3	$105.32	5.634%	$111.2537	$111.25	$111.25	$111.30
Purchase #4	$139.60	5.424%	$147.1719	$147.17	$147.15	$147.20
Purchase #5	$211.72	10.770%	$234.5222	$234.52	$234.50	$234.50
Purchase #6	$5.56	11.151%	$6.18	$6.18	$6.20	$6.20
Purchase #7	$237.66	3.351%	$245.624	$245.62	$245.60	$245.60
7 purchase totals =	$893.05		$953.8243	$953.82	$953.80	$953.80