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	$92.75	6.202%	$98.5024	$98.50	$98.50	$98.50
Purchase #2	$117.56	7.557%	$126.444	$126.44	$126.45	$126.40
Purchase #3	$84.43	6.534%	$89.9467	$89.95	$89.95	$89.90
Purchase #4	$72.97	10.470%	$80.61	$80.61	$80.60	$80.60
Purchase #5	$80.66	11.626%	$90.0375	$90.04	$90.05	$90.00
Purchase #6	$161.49	3.401%	$166.9823	$166.98	$167.00	$167.00
Purchase #7	$126.29	13.396%	$143.2078	$143.21	$143.20	$143.20
7 purchase totals =	$736.15		$795.7307	$795.73	$795.75	$795.60