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	$18.95	7.408%	$20.3538	$20.35	$20.35	$20.40
Purchase #2	$248.72	11.289%	$276.798	$276.80	$276.80	$276.80
Purchase #3	$105.25	5.709%	$111.2587	$111.26	$111.25	$111.30
Purchase #4	$174.46	12.368%	$196.0372	$196.04	$196.05	$196.00
Purchase #5	$205.93	8.828%	$224.1095	$224.11	$224.10	$224.10
Purchase #6	$249.53	12.117%	$279.7656	$279.77	$279.75	$279.80
Purchase #7	$18.94	3.528%	$19.6082	$19.61	$19.60	$19.60
7 purchase totals =	$1,021.78		$1,127.9310	$1,127.94	$1,127.90	$1,128.00