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	$92.43	8.153%	$99.9658	$99.97	$99.95	$100.00
Purchase #2	$38.48	8.408%	$41.7154	$41.72	$41.70	$41.70
Purchase #3	$88.91	8.842%	$96.7714	$96.77	$96.75	$96.80
Purchase #4	$104.78	6.652%	$111.75	$111.75	$111.75	$111.80
Purchase #5	$221.49	13.725%	$251.8895	$251.89	$251.90	$251.90
Purchase #6	$38.31	12.549%	$43.1175	$43.12	$43.10	$43.10
Purchase #7	$15.33	12.571%	$17.2571	$17.26	$17.25	$17.30
7 purchase totals =	$599.73		$662.4667	$662.48	$662.40	$662.60