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	$105.46	12.377%	$118.5128	$118.51	$118.50	$118.50
Purchase #2	$232.85	13.514%	$264.3173	$264.32	$264.30	$264.30
Purchase #3	$104.88	6.459%	$111.6542	$111.65	$111.65	$111.70
Purchase #4	$157.38	13.181%	$178.1243	$178.12	$178.10	$178.10
Purchase #5	$239.53	9.577%	$262.4698	$262.47	$262.45	$262.50
Purchase #6	$217.69	3.320%	$224.9173	$224.92	$224.90	$224.90
Purchase #7	$26.44	6.413%	$28.1356	$28.14	$28.15	$28.10
7 purchase totals =	$1,084.23		$1,188.1313	$1,188.13	$1,188.05	$1,188.10