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	$93.84	7.271%	$100.6631	$100.66	$100.65	$100.70
Purchase #2	$155.32	4.594%	$162.4554	$162.46	$162.45	$162.50
Purchase #3	$236.92	12.130%	$265.6584	$265.66	$265.65	$265.70
Purchase #4	$159.61	11.185%	$177.4624	$177.46	$177.45	$177.50
Purchase #5	$109.59	6.865%	$117.1134	$117.11	$117.10	$117.10
Purchase #6	$37.84	11.736%	$42.2809	$42.28	$42.30	$42.30
Purchase #7	$18.84	12.856%	$21.2621	$21.26	$21.25	$21.30
7 purchase totals =	$811.96		$886.8957	$886.89	$886.85	$887.10