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	$150.48	12.170%	$168.7934	$168.79	$168.80	$168.80
Purchase #2	$66.98	6.428%	$71.2855	$71.29	$71.30	$71.30
Purchase #3	$130.88	9.726%	$143.6094	$143.61	$143.60	$143.60
Purchase #4	$89.89	4.238%	$93.6995	$93.70	$93.70	$93.70
Purchase #5	$97.55	8.449%	$105.792	$105.79	$105.80	$105.80
Purchase #6	$41.25	6.286%	$43.843	$43.84	$43.85	$43.80
Purchase #7	$21.96	11.402%	$24.4639	$24.46	$24.45	$24.50
7 purchase totals =	$598.99		$651.4867	$651.48	$651.50	$651.50