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	$231.44	7.792%	$249.4738	$249.47	$249.45	$249.50
Purchase #2	$11.49	3.462%	$11.8878	$11.89	$11.90	$11.90
Purchase #3	$225.66	7.482%	$242.5439	$242.54	$242.55	$242.50
Purchase #4	$243.74	13.351%	$276.2817	$276.28	$276.30	$276.30
Purchase #5	$51.81	9.410%	$56.6853	$56.69	$56.70	$56.70
Purchase #6	$247.26	3.514%	$255.9487	$255.95	$255.95	$255.90
Purchase #7	$5.38	12.822%	$6.0698	$6.07	$6.05	$6.10
7 purchase totals =	$1,016.78		$1,098.8910	$1,098.89	$1,098.90	$1,098.90