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	$89.27	12.410%	$100.3484	$100.35	$100.35	$100.30
Purchase #2	$156.94	11.836%	$175.5154	$175.52	$175.50	$175.50
Purchase #3	$168.79	3.794%	$175.1939	$175.19	$175.20	$175.20
Purchase #4	$200.60	11.754%	$224.1785	$224.18	$224.20	$224.20
Purchase #5	$74.63	10.619%	$82.555	$82.56	$82.55	$82.60
Purchase #6	$78.67	13.130%	$88.9994	$89.00	$89.00	$89.00
Purchase #7	$134.88	13.744%	$153.4179	$153.42	$153.40	$153.40
7 purchase totals =	$903.78		$1,000.2085	$1,000.22	$1,000.20	$1,000.20