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	$227.71	9.126%	$248.4908	$248.49	$248.50	$248.50
Purchase #2	$242.42	3.164%	$250.0902	$250.09	$250.10	$250.10
Purchase #3	$99.87	11.537%	$111.392	$111.39	$111.40	$111.40
Purchase #4	$56.91	3.402%	$58.8461	$58.85	$58.85	$58.80
Purchase #5	$29.34	6.647%	$31.2902	$31.29	$31.30	$31.30
Purchase #6	$215.61	6.404%	$229.4177	$229.42	$229.40	$229.40
Purchase #7	$170.43	6.222%	$181.0342	$181.03	$181.05	$181.00
7 purchase totals =	$1,042.29		$1,110.5612	$1,110.56	$1,110.60	$1,110.50