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	$96.79	9.839%	$106.3132	$106.31	$106.30	$106.30
Purchase #2	$168.95	12.794%	$190.5655	$190.57	$190.55	$190.60
Purchase #3	$241.37	9.740%	$264.8794	$264.88	$264.90	$264.90
Purchase #4	$155.51	11.158%	$172.8618	$172.86	$172.85	$172.90
Purchase #5	$105.33	5.852%	$111.4939	$111.49	$111.50	$111.50
Purchase #6	$12.37	10.216%	$13.6337	$13.63	$13.65	$13.60
Purchase #7	$35.36	10.799%	$39.1785	$39.18	$39.20	$39.20
7 purchase totals =	$815.68		$898.9260	$898.92	$898.95	$899.00