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	$110.85	8.496%	$120.2678	$120.27	$120.25	$120.30
Purchase #2	$14.65	13.169%	$16.5793	$16.58	$16.60	$16.60
Purchase #3	$178.86	8.809%	$194.6158	$194.62	$194.60	$194.60
Purchase #4	$141.34	7.756%	$152.3023	$152.30	$152.30	$152.30
Purchase #5	$95.78	3.749%	$99.3708	$99.37	$99.35	$99.40
Purchase #6	$124.25	3.262%	$128.303	$128.30	$128.30	$128.30
Purchase #7	$99.89	5.637%	$105.5208	$105.52	$105.50	$105.50
7 purchase totals =	$765.62		$816.9598	$816.96	$816.90	$817.00