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	$9.86	3.228%	$10.1783	$10.18	$10.20	$10.20
Purchase #2	$152.81	9.456%	$167.2597	$167.26	$167.25	$167.30
Purchase #3	$97.63	13.872%	$111.1732	$111.17	$111.15	$111.20
Purchase #4	$212.50	9.776%	$233.274	$233.27	$233.25	$233.30
Purchase #5	$128.80	4.116%	$134.1014	$134.10	$134.10	$134.10
Purchase #6	$103.99	9.739%	$114.1176	$114.12	$114.10	$114.10
Purchase #7	$120.91	9.138%	$131.9588	$131.96	$131.95	$132.00
7 purchase totals =	$826.50		$902.0630	$902.06	$902.00	$902.20