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	$18.50	11.180%	$20.5683	$20.57	$20.55	$20.60
Purchase #2	$194.54	10.771%	$215.4939	$215.49	$215.50	$215.50
Purchase #3	$21.85	11.111%	$24.2778	$24.28	$24.30	$24.30
Purchase #4	$209.36	12.207%	$234.9166	$234.92	$234.90	$234.90
Purchase #5	$74.49	10.640%	$82.4157	$82.42	$82.40	$82.40
Purchase #6	$45.95	12.672%	$51.7728	$51.77	$51.75	$51.80
Purchase #7	$124.83	11.233%	$138.8522	$138.85	$138.85	$138.90
7 purchase totals =	$689.52		$768.2973	$768.30	$768.25	$768.40