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	$128.30	10.502%	$141.7741	$141.77	$141.75	$141.80
Purchase #2	$168.33	10.857%	$186.6056	$186.61	$186.60	$186.60
Purchase #3	$245.97	11.599%	$274.5001	$274.50	$274.50	$274.50
Purchase #4	$52.55	10.667%	$58.1555	$58.16	$58.15	$58.20
Purchase #5	$187.42	3.370%	$193.7361	$193.74	$193.75	$193.70
Purchase #6	$176.52	10.347%	$194.7845	$194.78	$194.80	$194.80
Purchase #7	$96.59	4.141%	$100.5898	$100.59	$100.60	$100.60
7 purchase totals =	$1,055.68		$1,150.1457	$1,150.15	$1,150.15	$1,150.20