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	$47.41	11.138%	$52.6905	$52.69	$52.70	$52.70
Purchase #2	$115.66	11.409%	$128.8556	$128.86	$128.85	$128.90
Purchase #3	$219.90	12.748%	$247.9329	$247.93	$247.95	$247.90
Purchase #4	$97.40	3.154%	$100.472	$100.47	$100.45	$100.50
Purchase #5	$40.93	10.583%	$45.2616	$45.26	$45.25	$45.30
Purchase #6	$166.81	13.518%	$189.3594	$189.36	$189.35	$189.40
Purchase #7	$232.47	5.523%	$245.3093	$245.31	$245.30	$245.30
7 purchase totals =	$920.58		$1,009.8813	$1,009.88	$1,009.85	$1,010.00