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	$124.85	13.601%	$141.8308	$141.83	$141.85	$141.80
Purchase #2	$49.82	7.707%	$53.6596	$53.66	$53.65	$53.70
Purchase #3	$153.28	10.810%	$169.8496	$169.85	$169.85	$169.80
Purchase #4	$98.91	11.809%	$110.5903	$110.59	$110.60	$110.60
Purchase #5	$86.76	3.451%	$89.7541	$89.75	$89.75	$89.80
Purchase #6	$225.61	12.531%	$253.8812	$253.88	$253.90	$253.90
Purchase #7	$71.51	9.357%	$78.2012	$78.20	$78.20	$78.20
7 purchase totals =	$810.74		$897.7668	$897.76	$897.80	$897.80