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	$59.56	12.104%	$66.7691	$66.77	$66.75	$66.80
Purchase #2	$95.38	13.298%	$108.0636	$108.06	$108.05	$108.10
Purchase #3	$17.92	5.360%	$18.8805	$18.88	$18.90	$18.90
Purchase #4	$33.40	12.430%	$37.5516	$37.55	$37.55	$37.60
Purchase #5	$41.32	6.795%	$44.1277	$44.13	$44.15	$44.10
Purchase #6	$186.47	5.430%	$196.5953	$196.60	$196.60	$196.60
Purchase #7	$34.55	3.104%	$35.6224	$35.62	$35.60	$35.60
7 purchase totals =	$468.60		$507.6102	$507.61	$507.60	$507.70