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	$41.33	8.423%	$44.8112	$44.81	$44.80	$44.80
Purchase #2	$210.39	11.756%	$235.1234	$235.12	$235.10	$235.10
Purchase #3	$189.67	3.719%	$196.7238	$196.72	$196.70	$196.70
Purchase #4	$60.37	12.282%	$67.7846	$67.78	$67.80	$67.80
Purchase #5	$229.59	9.324%	$250.997	$251.00	$251.00	$251.00
Purchase #6	$131.52	6.676%	$140.3003	$140.30	$140.30	$140.30
Purchase #7	$128.30	13.635%	$145.7937	$145.79	$145.80	$145.80
7 purchase totals =	$991.17		$1,081.5340	$1,081.52	$1,081.50	$1,081.50