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	$7.89	13.109%	$8.9243	$8.92	$8.90	$8.90
Purchase #2	$200.59	9.406%	$219.4575	$219.46	$219.45	$219.50
Purchase #3	$122.32	4.570%	$127.91	$127.91	$127.90	$127.90
Purchase #4	$175.65	5.611%	$185.5057	$185.51	$185.50	$185.50
Purchase #5	$81.42	10.866%	$90.2671	$90.27	$90.25	$90.30
Purchase #6	$214.35	5.446%	$226.0235	$226.02	$226.00	$226.00
Purchase #7	$174.83	11.705%	$195.2939	$195.29	$195.30	$195.30
7 purchase totals =	$977.05		$1,053.3820	$1,053.38	$1,053.30	$1,053.40