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	$136.54	4.361%	$142.4945	$142.49	$142.50	$142.50
Purchase #2	$183.28	13.769%	$208.5158	$208.52	$208.50	$208.50
Purchase #3	$244.65	13.819%	$278.4582	$278.46	$278.45	$278.50
Purchase #4	$100.52	6.556%	$107.1101	$107.11	$107.10	$107.10
Purchase #5	$131.30	10.735%	$145.3951	$145.40	$145.40	$145.40
Purchase #6	$100.30	12.628%	$112.9659	$112.97	$112.95	$113.00
Purchase #7	$87.89	10.227%	$96.8785	$96.88	$96.90	$96.90
7 purchase totals =	$984.48		$1,091.8181	$1,091.83	$1,091.80	$1,091.90