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	$235.66	10.427%	$260.2323	$260.23	$260.25	$260.20
Purchase #2	$127.85	12.259%	$143.5231	$143.52	$143.50	$143.50
Purchase #3	$51.92	6.817%	$55.4594	$55.46	$55.45	$55.50
Purchase #4	$134.96	11.712%	$150.7665	$150.77	$150.75	$150.80
Purchase #5	$89.86	12.657%	$101.2336	$101.23	$101.25	$101.20
Purchase #6	$28.40	11.487%	$31.6623	$31.66	$31.65	$31.70
Purchase #7	$105.31	5.619%	$111.2274	$111.23	$111.25	$111.20
7 purchase totals =	$773.96		$854.1046	$854.10	$854.10	$854.10