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	$182.91	4.684%	$191.4775	$191.48	$191.50	$191.50
Purchase #2	$201.85	6.408%	$214.7845	$214.78	$214.80	$214.80
Purchase #3	$107.54	4.116%	$111.9663	$111.97	$111.95	$112.00
Purchase #4	$245.87	13.693%	$279.537	$279.54	$279.55	$279.50
Purchase #5	$110.45	11.396%	$123.0369	$123.04	$123.05	$123.00
Purchase #6	$240.32	13.222%	$272.0951	$272.10	$272.10	$272.10
Purchase #7	$79.88	11.369%	$88.9616	$88.96	$88.95	$89.00
7 purchase totals =	$1,168.82		$1,281.8589	$1,281.87	$1,281.90	$1,281.90