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	$56.68	4.120%	$59.0152	$59.02	$59.00	$59.00
Purchase #2	$207.63	10.352%	$229.1239	$229.12	$229.10	$229.10
Purchase #3	$189.94	10.711%	$210.2845	$210.28	$210.30	$210.30
Purchase #4	$24.66	13.156%	$27.9043	$27.90	$27.90	$27.90
Purchase #5	$141.73	9.799%	$155.6181	$155.62	$155.60	$155.60
Purchase #6	$141.84	7.481%	$152.4511	$152.45	$152.45	$152.50
Purchase #7	$42.79	13.666%	$48.6377	$48.64	$48.65	$48.60
7 purchase totals =	$805.27		$883.0348	$883.03	$883.00	$883.00