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	$181.48	13.420%	$205.8346	$205.83	$205.85	$205.80
Purchase #2	$154.48	10.710%	$171.0248	$171.02	$171.00	$171.00
Purchase #3	$219.51	4.483%	$229.3506	$229.35	$229.35	$229.40
Purchase #4	$59.86	13.412%	$67.8884	$67.89	$67.90	$67.90
Purchase #5	$124.78	11.750%	$139.4417	$139.44	$139.45	$139.40
Purchase #6	$24.37	3.844%	$25.3068	$25.31	$25.30	$25.30
Purchase #7	$23.75	11.264%	$26.4252	$26.43	$26.45	$26.40
7 purchase totals =	$788.23		$865.2721	$865.27	$865.30	$865.20