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	$35.46	8.104%	$38.3337	$38.33	$38.35	$38.30
Purchase #2	$80.75	6.198%	$85.7549	$85.75	$85.75	$85.80
Purchase #3	$158.34	11.316%	$176.2578	$176.26	$176.25	$176.30
Purchase #4	$93.50	11.406%	$104.1646	$104.16	$104.15	$104.20
Purchase #5	$88.35	13.619%	$100.3824	$100.38	$100.40	$100.40
Purchase #6	$250.64	8.669%	$272.368	$272.37	$272.35	$272.40
Purchase #7	$235.72	9.805%	$258.8323	$258.83	$258.85	$258.80
7 purchase totals =	$942.76		$1,036.0937	$1,036.08	$1,036.10	$1,036.20