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	$17.33	12.221%	$19.4479	$19.45	$19.45	$19.40
Purchase #2	$66.25	6.345%	$70.4536	$70.45	$70.45	$70.50
Purchase #3	$185.86	10.564%	$205.4943	$205.49	$205.50	$205.50
Purchase #4	$125.63	10.831%	$139.237	$139.24	$139.25	$139.20
Purchase #5	$228.43	3.539%	$236.5141	$236.51	$236.50	$236.50
Purchase #6	$168.89	9.238%	$184.4921	$184.49	$184.50	$184.50
Purchase #7	$41.76	4.322%	$43.5649	$43.56	$43.55	$43.60
7 purchase totals =	$834.15		$899.2039	$899.19	$899.20	$899.20