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	$67.72	4.141%	$70.5243	$70.52	$70.50	$70.50
Purchase #2	$58.76	11.361%	$65.4357	$65.44	$65.45	$65.40
Purchase #3	$215.42	8.294%	$233.2869	$233.29	$233.30	$233.30
Purchase #4	$111.50	9.666%	$122.2776	$122.28	$122.30	$122.30
Purchase #5	$156.66	7.211%	$167.9568	$167.96	$167.95	$168.00
Purchase #6	$151.44	4.341%	$158.014	$158.01	$158.00	$158.00
Purchase #7	$248.45	10.470%	$274.4627	$274.46	$274.45	$274.50
7 purchase totals =	$1,009.95		$1,091.9580	$1,091.96	$1,091.95	$1,092.00