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	$74.40	10.424%	$82.1555	$82.16	$82.15	$82.20
Purchase #2	$36.75	4.652%	$38.4596	$38.46	$38.45	$38.50
Purchase #3	$227.28	5.304%	$239.3349	$239.33	$239.35	$239.30
Purchase #4	$48.37	10.153%	$53.281	$53.28	$53.30	$53.30
Purchase #5	$165.84	8.275%	$179.5633	$179.56	$179.55	$179.60
Purchase #6	$237.60	5.548%	$250.782	$250.78	$250.80	$250.80
Purchase #7	$125.99	10.682%	$139.4483	$139.45	$139.45	$139.40
7 purchase totals =	$916.23		$983.0246	$983.02	$983.05	$983.10