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	$160.55	12.536%	$180.6765	$180.68	$180.70	$180.70
Purchase #2	$231.65	8.532%	$251.4144	$251.41	$251.40	$251.40
Purchase #3	$87.40	3.622%	$90.5656	$90.57	$90.55	$90.60
Purchase #4	$36.33	8.152%	$39.2916	$39.29	$39.30	$39.30
Purchase #5	$218.83	3.204%	$225.8413	$225.84	$225.85	$225.80
Purchase #6	$171.83	11.847%	$192.1867	$192.19	$192.20	$192.20
Purchase #7	$40.74	4.215%	$42.4572	$42.46	$42.45	$42.50
7 purchase totals =	$947.33		$1,022.4333	$1,022.44	$1,022.45	$1,022.50