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	$38.52	5.153%	$40.5049	$40.50	$40.50	$40.50
Purchase #2	$91.91	10.327%	$101.4015	$101.40	$101.40	$101.40
Purchase #3	$117.63	8.356%	$127.4592	$127.46	$127.45	$127.50
Purchase #4	$212.50	6.489%	$226.2891	$226.29	$226.30	$226.30
Purchase #5	$96.77	13.526%	$109.8591	$109.86	$109.85	$109.90
Purchase #6	$210.73	7.125%	$225.7445	$225.74	$225.75	$225.70
Purchase #7	$52.67	10.773%	$58.3441	$58.34	$58.35	$58.30
7 purchase totals =	$820.73		$889.6024	$889.59	$889.60	$889.60