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	$221.85	6.332%	$235.8975	$235.90	$235.90	$235.90
Purchase #2	$41.78	10.853%	$46.3144	$46.31	$46.30	$46.30
Purchase #3	$80.43	6.363%	$85.5478	$85.55	$85.55	$85.50
Purchase #4	$37.42	13.776%	$42.575	$42.58	$42.60	$42.60
Purchase #5	$229.72	8.837%	$250.0204	$250.02	$250.00	$250.00
Purchase #6	$226.62	9.784%	$248.7925	$248.79	$248.80	$248.80
Purchase #7	$246.41	9.238%	$269.1734	$269.17	$269.15	$269.20
7 purchase totals =	$1,084.23		$1,178.3210	$1,178.32	$1,178.30	$1,178.30