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	$54.64	9.810%	$60.0002	$60.00	$60.00	$60.00
Purchase #2	$182.68	10.830%	$202.4642	$202.46	$202.45	$202.50
Purchase #3	$235.71	10.439%	$260.3158	$260.32	$260.30	$260.30
Purchase #4	$145.47	10.554%	$160.8229	$160.82	$160.80	$160.80
Purchase #5	$101.31	10.449%	$111.8959	$111.90	$111.90	$111.90
Purchase #6	$68.91	13.516%	$78.2239	$78.22	$78.20	$78.20
Purchase #7	$190.84	9.804%	$209.55	$209.55	$209.55	$209.60
7 purchase totals =	$979.56		$1,083.2729	$1,083.27	$1,083.20	$1,083.30