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	$29.89	11.354%	$33.2837	$33.28	$33.30	$33.30
Purchase #2	$208.90	6.666%	$222.8253	$222.83	$222.85	$222.80
Purchase #3	$249.46	10.612%	$275.9327	$275.93	$275.95	$275.90
Purchase #4	$43.63	10.538%	$48.2277	$48.23	$48.25	$48.20
Purchase #5	$32.65	5.600%	$34.4784	$34.48	$34.50	$34.50
Purchase #6	$127.52	7.490%	$137.0712	$137.07	$137.05	$137.10
Purchase #7	$104.53	6.128%	$110.9356	$110.94	$110.95	$110.90
7 purchase totals =	$796.58		$862.7546	$862.76	$862.85	$862.70