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	$232.54	10.274%	$256.4312	$256.43	$256.45	$256.40
Purchase #2	$221.45	6.653%	$236.1831	$236.18	$236.20	$236.20
Purchase #3	$234.81	8.816%	$255.5108	$255.51	$255.50	$255.50
Purchase #4	$29.26	5.653%	$30.9141	$30.91	$30.90	$30.90
Purchase #5	$89.90	10.103%	$98.9826	$98.98	$99.00	$99.00
Purchase #6	$37.60	12.727%	$42.3854	$42.39	$42.40	$42.40
Purchase #7	$120.39	12.221%	$135.1029	$135.10	$135.10	$135.10
7 purchase totals =	$965.95		$1,055.5101	$1,055.50	$1,055.55	$1,055.50