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	$29.78	13.380%	$33.7646	$33.76	$33.75	$33.80
Purchase #2	$79.47	10.625%	$87.9137	$87.91	$87.90	$87.90
Purchase #3	$184.76	8.420%	$200.3168	$200.32	$200.30	$200.30
Purchase #4	$117.93	11.271%	$131.2219	$131.22	$131.20	$131.20
Purchase #5	$45.91	7.579%	$49.3895	$49.39	$49.40	$49.40
Purchase #6	$135.35	12.786%	$152.6559	$152.66	$152.65	$152.70
Purchase #7	$237.66	11.757%	$265.6017	$265.60	$265.60	$265.60
7 purchase totals =	$830.86		$920.8641	$920.86	$920.80	$920.90