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	$137.58	3.871%	$142.9057	$142.91	$142.90	$142.90
Purchase #2	$107.44	3.778%	$111.4991	$111.50	$111.50	$111.50
Purchase #3	$30.95	12.713%	$34.8847	$34.88	$34.90	$34.90
Purchase #4	$87.66	5.506%	$92.4866	$92.49	$92.50	$92.50
Purchase #5	$134.45	9.470%	$147.1824	$147.18	$147.20	$147.20
Purchase #6	$7.50	11.746%	$8.381	$8.38	$8.40	$8.40
Purchase #7	$232.74	7.623%	$250.4818	$250.48	$250.50	$250.50
7 purchase totals =	$738.32		$787.8213	$787.82	$787.90	$787.90