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	$170.40	11.687%	$190.3146	$190.31	$190.30	$190.30
Purchase #2	$168.93	6.142%	$179.3057	$179.31	$179.30	$179.30
Purchase #3	$158.34	13.773%	$180.1482	$180.15	$180.15	$180.10
Purchase #4	$67.73	5.788%	$71.6502	$71.65	$71.65	$71.70
Purchase #5	$132.81	7.207%	$142.3816	$142.38	$142.40	$142.40
Purchase #6	$128.27	3.160%	$132.3233	$132.32	$132.30	$132.30
Purchase #7	$65.78	3.670%	$68.1941	$68.19	$68.20	$68.20
7 purchase totals =	$892.26		$964.3177	$964.31	$964.30	$964.30