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	$133.47	4.373%	$139.3066	$139.31	$139.30	$139.30
Purchase #2	$198.29	3.496%	$205.2222	$205.22	$205.20	$205.20
Purchase #3	$176.25	6.140%	$187.0718	$187.07	$187.05	$187.10
Purchase #4	$65.38	11.861%	$73.1347	$73.13	$73.15	$73.10
Purchase #5	$203.61	12.103%	$228.2529	$228.25	$228.25	$228.30
Purchase #6	$35.25	9.152%	$38.4761	$38.48	$38.50	$38.50
Purchase #7	$173.89	6.288%	$184.8242	$184.82	$184.80	$184.80
7 purchase totals =	$986.14		$1,056.2885	$1,056.28	$1,056.25	$1,056.30