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	$43.43	3.636%	$45.0091	$45.01	$45.00	$45.00
Purchase #2	$52.89	12.710%	$59.6123	$59.61	$59.60	$59.60
Purchase #3	$51.90	3.757%	$53.8499	$53.85	$53.85	$53.80
Purchase #4	$130.83	10.234%	$144.2191	$144.22	$144.20	$144.20
Purchase #5	$147.45	8.225%	$159.5778	$159.58	$159.60	$159.60
Purchase #6	$171.91	13.227%	$194.6485	$194.65	$194.65	$194.60
Purchase #7	$29.95	11.283%	$33.3293	$33.33	$33.35	$33.30
7 purchase totals =	$628.36		$690.2460	$690.25	$690.25	$690.10