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	$12.90	7.268%	$13.8376	$13.84	$13.85	$13.80
Purchase #2	$161.81	10.485%	$178.7758	$178.78	$178.80	$178.80
Purchase #3	$92.44	9.807%	$101.5056	$101.51	$101.50	$101.50
Purchase #4	$48.61	12.790%	$54.8272	$54.83	$54.85	$54.80
Purchase #5	$38.93	4.870%	$40.8259	$40.83	$40.85	$40.80
Purchase #6	$197.93	5.304%	$208.4282	$208.43	$208.45	$208.40
Purchase #7	$88.39	3.199%	$91.2176	$91.22	$91.20	$91.20
7 purchase totals =	$641.01		$689.4179	$689.44	$689.50	$689.30