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	$73.29	12.599%	$82.5238	$82.52	$82.50	$82.50
Purchase #2	$26.85	12.347%	$30.1652	$30.17	$30.15	$30.20
Purchase #3	$241.67	11.230%	$268.8095	$268.81	$268.80	$268.80
Purchase #4	$54.55	8.401%	$59.1327	$59.13	$59.15	$59.10
Purchase #5	$176.93	4.262%	$184.4708	$184.47	$184.45	$184.50
Purchase #6	$114.94	3.355%	$118.7962	$118.80	$118.80	$118.80
Purchase #7	$74.32	11.466%	$82.8415	$82.84	$82.85	$82.80
7 purchase totals =	$762.55		$826.7397	$826.74	$826.70	$826.70