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	$67.65	6.740%	$72.2096	$72.21	$72.20	$72.20
Purchase #2	$104.67	4.222%	$109.0892	$109.09	$109.10	$109.10
Purchase #3	$139.27	11.126%	$154.7652	$154.77	$154.75	$154.80
Purchase #4	$104.51	10.617%	$115.6058	$115.61	$115.60	$115.60
Purchase #5	$127.61	13.399%	$144.7085	$144.71	$144.70	$144.70
Purchase #6	$11.36	9.376%	$12.4251	$12.43	$12.45	$12.40
Purchase #7	$75.52	4.722%	$79.0861	$79.09	$79.10	$79.10
7 purchase totals =	$630.59		$687.8895	$687.91	$687.90	$687.90