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	$90.50	9.814%	$99.3817	$99.38	$99.40	$99.40
Purchase #2	$104.77	9.670%	$114.9013	$114.90	$114.90	$114.90
Purchase #3	$120.90	5.108%	$127.0756	$127.08	$127.10	$127.10
Purchase #4	$132.54	6.828%	$141.5898	$141.59	$141.60	$141.60
Purchase #5	$14.47	10.874%	$16.0435	$16.04	$16.05	$16.00
Purchase #6	$98.53	10.648%	$109.0215	$109.02	$109.00	$109.00
Purchase #7	$63.36	9.322%	$69.2664	$69.27	$69.25	$69.30
7 purchase totals =	$625.07		$677.2798	$677.28	$677.30	$677.30