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	$82.88	10.851%	$91.8733	$91.87	$91.85	$91.90
Purchase #2	$214.25	11.161%	$238.1624	$238.16	$238.15	$238.20
Purchase #3	$174.51	5.631%	$184.3367	$184.34	$184.35	$184.30
Purchase #4	$234.32	8.502%	$254.2419	$254.24	$254.25	$254.20
Purchase #5	$111.38	12.354%	$125.1399	$125.14	$125.15	$125.10
Purchase #6	$64.59	4.108%	$67.2434	$67.24	$67.25	$67.20
Purchase #7	$168.45	4.136%	$175.4171	$175.42	$175.40	$175.40
7 purchase totals =	$1,050.38		$1,136.4147	$1,136.41	$1,136.40	$1,136.30