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	$137.99	10.507%	$152.4886	$152.49	$152.50	$152.50
Purchase #2	$45.90	4.868%	$48.1344	$48.13	$48.15	$48.10
Purchase #3	$229.87	3.640%	$238.2373	$238.24	$238.25	$238.20
Purchase #4	$80.72	11.631%	$90.1085	$90.11	$90.10	$90.10
Purchase #5	$240.36	11.824%	$268.7802	$268.78	$268.80	$268.80
Purchase #6	$77.58	7.226%	$83.1859	$83.19	$83.20	$83.20
Purchase #7	$145.45	8.226%	$157.4147	$157.41	$157.40	$157.40
7 purchase totals =	$957.87		$1,038.3496	$1,038.35	$1,038.40	$1,038.30