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	$20.58	8.680%	$22.3663	$22.37	$22.35	$22.40
Purchase #2	$49.47	6.190%	$52.5322	$52.53	$52.55	$52.50
Purchase #3	$161.48	13.385%	$183.0941	$183.09	$183.10	$183.10
Purchase #4	$60.63	3.236%	$62.592	$62.59	$62.60	$62.60
Purchase #5	$34.69	3.381%	$35.8629	$35.86	$35.85	$35.90
Purchase #6	$52.97	7.766%	$57.0837	$57.08	$57.10	$57.10
Purchase #7	$52.51	13.293%	$59.4902	$59.49	$59.50	$59.50
7 purchase totals =	$432.33		$473.0214	$473.01	$473.05	$473.10