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	$245.50	12.268%	$275.6179	$275.62	$275.60	$275.60
Purchase #2	$109.33	6.643%	$116.5928	$116.59	$116.60	$116.60
Purchase #3	$124.54	12.363%	$139.9369	$139.94	$139.95	$139.90
Purchase #4	$100.31	8.489%	$108.8253	$108.83	$108.85	$108.80
Purchase #5	$118.57	3.574%	$122.8077	$122.81	$122.80	$122.80
Purchase #6	$227.55	11.729%	$254.2393	$254.24	$254.25	$254.20
Purchase #7	$34.57	13.646%	$39.2874	$39.29	$39.30	$39.30
7 purchase totals =	$960.37		$1,057.3073	$1,057.32	$1,057.35	$1,057.20