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	$221.32	6.227%	$235.1016	$235.10	$235.10	$235.10
Purchase #2	$130.84	11.462%	$145.8369	$145.84	$145.85	$145.80
Purchase #3	$108.52	13.587%	$123.2646	$123.26	$123.25	$123.30
Purchase #4	$72.74	10.545%	$80.4104	$80.41	$80.40	$80.40
Purchase #5	$66.67	8.461%	$72.3109	$72.31	$72.30	$72.30
Purchase #6	$143.48	12.761%	$161.7895	$161.79	$161.80	$161.80
Purchase #7	$146.96	8.780%	$159.8631	$159.86	$159.85	$159.90
7 purchase totals =	$890.53		$978.5770	$978.57	$978.55	$978.60