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	$127.42	11.354%	$141.8873	$141.89	$141.90	$141.90
Purchase #2	$160.96	3.550%	$166.6741	$166.67	$166.65	$166.70
Purchase #3	$83.64	12.116%	$93.7738	$93.77	$93.75	$93.80
Purchase #4	$20.77	4.671%	$21.7402	$21.74	$21.75	$21.70
Purchase #5	$196.69	8.684%	$213.7706	$213.77	$213.75	$213.80
Purchase #6	$93.96	6.764%	$100.3155	$100.32	$100.30	$100.30
Purchase #7	$60.65	7.195%	$65.0138	$65.01	$65.00	$65.00
7 purchase totals =	$744.09		$803.1753	$803.17	$803.10	$803.20