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	$88.46	13.414%	$100.326	$100.33	$100.35	$100.30
Purchase #2	$241.82	3.454%	$250.1725	$250.17	$250.15	$250.20
Purchase #3	$172.43	3.639%	$178.7047	$178.70	$178.70	$178.70
Purchase #4	$172.32	10.680%	$190.7238	$190.72	$190.70	$190.70
Purchase #5	$154.94	7.793%	$167.0145	$167.01	$167.00	$167.00
Purchase #6	$140.80	13.420%	$159.6954	$159.70	$159.70	$159.70
Purchase #7	$57.35	12.477%	$64.5056	$64.51	$64.50	$64.50
7 purchase totals =	$1,028.12		$1,111.1425	$1,111.14	$1,111.10	$1,111.10