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	$11.27	9.869%	$12.3822	$12.38	$12.40	$12.40
Purchase #2	$57.61	5.286%	$60.6553	$60.66	$60.65	$60.70
Purchase #3	$31.96	4.723%	$33.4695	$33.47	$33.45	$33.50
Purchase #4	$85.89	9.272%	$93.8537	$93.85	$93.85	$93.90
Purchase #5	$93.57	11.661%	$104.4812	$104.48	$104.50	$104.50
Purchase #6	$79.78	6.832%	$85.2306	$85.23	$85.25	$85.20
Purchase #7	$194.55	13.189%	$220.2092	$220.21	$220.20	$220.20
7 purchase totals =	$554.63		$610.2817	$610.28	$610.30	$610.40