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	$88.88	11.624%	$99.2114	$99.21	$99.20	$99.20
Purchase #2	$113.37	10.760%	$125.5686	$125.57	$125.55	$125.60
Purchase #3	$119.64	3.239%	$123.5151	$123.52	$123.50	$123.50
Purchase #4	$116.28	10.707%	$128.7301	$128.73	$128.75	$128.70
Purchase #5	$80.46	12.396%	$90.4338	$90.43	$90.45	$90.40
Purchase #6	$234.26	11.477%	$261.146	$261.15	$261.15	$261.10
Purchase #7	$200.31	5.451%	$211.2289	$211.23	$211.25	$211.20
7 purchase totals =	$953.20		$1,039.8339	$1,039.84	$1,039.85	$1,039.70