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	$37.55	5.402%	$39.5785	$39.58	$39.60	$39.60
Purchase #2	$107.83	4.283%	$112.4484	$112.45	$112.45	$112.40
Purchase #3	$137.76	11.187%	$153.1712	$153.17	$153.15	$153.20
Purchase #4	$124.73	13.123%	$141.0983	$141.10	$141.10	$141.10
Purchase #5	$155.30	10.520%	$171.6376	$171.64	$171.65	$171.60
Purchase #6	$161.57	12.809%	$182.2655	$182.27	$182.25	$182.30
Purchase #7	$86.49	11.398%	$96.3481	$96.35	$96.35	$96.30
7 purchase totals =	$811.23		$896.5476	$896.56	$896.55	$896.50