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	$81.68	10.668%	$90.3936	$90.39	$90.40	$90.40
Purchase #2	$145.86	3.342%	$150.7346	$150.73	$150.75	$150.70
Purchase #3	$100.90	9.651%	$110.6379	$110.64	$110.65	$110.60
Purchase #4	$75.57	7.548%	$81.274	$81.27	$81.25	$81.30
Purchase #5	$209.82	4.566%	$219.4004	$219.40	$219.40	$219.40
Purchase #6	$246.87	11.532%	$275.339	$275.34	$275.35	$275.30
Purchase #7	$48.81	4.316%	$50.9166	$50.92	$50.90	$50.90
7 purchase totals =	$909.51		$978.6961	$978.69	$978.70	$978.60