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	$186.60	13.580%	$211.9403	$211.94	$211.95	$211.90
Purchase #2	$240.59	4.766%	$252.0565	$252.06	$252.05	$252.10
Purchase #3	$45.78	4.346%	$47.7696	$47.77	$47.75	$47.80
Purchase #4	$128.66	6.736%	$137.3265	$137.33	$137.35	$137.30
Purchase #5	$37.38	7.298%	$40.108	$40.11	$40.10	$40.10
Purchase #6	$95.63	8.649%	$103.901	$103.90	$103.90	$103.90
Purchase #7	$32.55	13.856%	$37.0601	$37.06	$37.05	$37.10
7 purchase totals =	$767.19		$830.1620	$830.17	$830.15	$830.20