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	$61.65	7.665%	$66.3755	$66.38	$66.40	$66.40
Purchase #2	$96.33	3.425%	$99.6293	$99.63	$99.65	$99.60
Purchase #3	$124.86	11.368%	$139.0541	$139.05	$139.05	$139.10
Purchase #4	$27.74	12.127%	$31.104	$31.10	$31.10	$31.10
Purchase #5	$54.41	6.343%	$57.8612	$57.86	$57.85	$57.90
Purchase #6	$142.40	6.415%	$151.535	$151.54	$151.55	$151.50
Purchase #7	$107.39	13.633%	$122.0305	$122.03	$122.05	$122.00
7 purchase totals =	$614.78		$667.5896	$667.59	$667.65	$667.60