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	$124.45	3.299%	$128.5556	$128.56	$128.55	$128.60
Purchase #2	$75.67	10.858%	$83.8862	$83.89	$83.90	$83.90
Purchase #3	$176.68	6.192%	$187.62	$187.62	$187.60	$187.60
Purchase #4	$50.38	3.846%	$52.3176	$52.32	$52.30	$52.30
Purchase #5	$40.87	9.656%	$44.8164	$44.82	$44.80	$44.80
Purchase #6	$66.55	7.125%	$71.2917	$71.29	$71.30	$71.30
Purchase #7	$155.87	10.129%	$171.6581	$171.66	$171.65	$171.70
7 purchase totals =	$690.47		$740.1456	$740.16	$740.10	$740.20