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	$109.40	8.330%	$118.513	$118.51	$118.50	$118.50
Purchase #2	$38.88	10.849%	$43.0981	$43.10	$43.10	$43.10
Purchase #3	$21.28	10.554%	$23.5259	$23.53	$23.55	$23.50
Purchase #4	$92.75	12.385%	$104.2371	$104.24	$104.25	$104.20
Purchase #5	$179.54	6.198%	$190.6679	$190.67	$190.65	$190.70
Purchase #6	$17.54	11.494%	$19.556	$19.56	$19.55	$19.60
Purchase #7	$51.31	11.708%	$57.3174	$57.32	$57.30	$57.30
7 purchase totals =	$510.70		$556.9154	$556.93	$556.90	$556.90