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	$34.35	4.360%	$35.8477	$35.85	$35.85	$35.80
Purchase #2	$102.28	11.586%	$114.1302	$114.13	$114.15	$114.10
Purchase #3	$10.34	4.607%	$10.8164	$10.82	$10.80	$10.80
Purchase #4	$96.41	13.196%	$109.1323	$109.13	$109.15	$109.10
Purchase #5	$84.96	3.119%	$87.6099	$87.61	$87.60	$87.60
Purchase #6	$68.70	3.704%	$71.2446	$71.24	$71.25	$71.20
Purchase #7	$71.87	11.286%	$79.9812	$79.98	$80.00	$80.00
7 purchase totals =	$468.91		$508.7623	$508.76	$508.80	$508.60