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	$79.89	13.270%	$90.4914	$90.49	$90.50	$90.50
Purchase #2	$116.89	9.157%	$127.5936	$127.59	$127.60	$127.60
Purchase #3	$103.39	4.204%	$107.7365	$107.74	$107.75	$107.70
Purchase #4	$113.56	9.865%	$124.7627	$124.76	$124.75	$124.80
Purchase #5	$170.93	4.321%	$178.3159	$178.32	$178.30	$178.30
Purchase #6	$242.66	5.717%	$256.5329	$256.53	$256.55	$256.50
Purchase #7	$72.26	11.814%	$80.7968	$80.80	$80.80	$80.80
7 purchase totals =	$899.58		$966.2298	$966.23	$966.25	$966.20