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	$19.44	7.334%	$20.8657	$20.87	$20.85	$20.90
Purchase #2	$145.73	13.558%	$165.4881	$165.49	$165.50	$165.50
Purchase #3	$177.91	11.408%	$198.206	$198.21	$198.20	$198.20
Purchase #4	$95.26	10.182%	$104.9594	$104.96	$104.95	$105.00
Purchase #5	$132.69	4.293%	$138.3864	$138.39	$138.40	$138.40
Purchase #6	$74.26	6.243%	$78.8961	$78.90	$78.90	$78.90
Purchase #7	$123.36	3.833%	$128.0884	$128.09	$128.10	$128.10
7 purchase totals =	$768.65		$834.8901	$834.91	$834.90	$835.00