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	$135.71	5.664%	$143.3966	$143.40	$143.40	$143.40
Purchase #2	$103.60	4.693%	$108.4619	$108.46	$108.45	$108.50
Purchase #3	$154.47	10.554%	$170.7728	$170.77	$170.75	$170.80
Purchase #4	$152.31	4.164%	$158.6522	$158.65	$158.65	$158.70
Purchase #5	$96.82	13.229%	$109.6283	$109.63	$109.65	$109.60
Purchase #6	$80.44	6.370%	$85.564	$85.56	$85.55	$85.60
Purchase #7	$81.51	3.559%	$84.4109	$84.41	$84.40	$84.40
7 purchase totals =	$804.86		$860.8867	$860.88	$860.85	$861.00