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	$35.81	6.778%	$38.2372	$38.24	$38.25	$38.20
Purchase #2	$52.98	7.638%	$57.0266	$57.03	$57.05	$57.00
Purchase #3	$168.66	13.369%	$191.2082	$191.21	$191.20	$191.20
Purchase #4	$179.94	5.826%	$190.4233	$190.42	$190.40	$190.40
Purchase #5	$184.43	8.131%	$199.426	$199.43	$199.45	$199.40
Purchase #6	$244.47	12.828%	$275.8306	$275.83	$275.85	$275.80
Purchase #7	$206.40	4.720%	$216.1421	$216.14	$216.15	$216.10
7 purchase totals =	$1,072.69		$1,168.2940	$1,168.30	$1,168.35	$1,168.10