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	$211.96	7.684%	$228.247	$228.25	$228.25	$228.20
Purchase #2	$41.33	9.315%	$45.1799	$45.18	$45.20	$45.20
Purchase #3	$90.49	11.291%	$100.7072	$100.71	$100.70	$100.70
Purchase #4	$23.90	7.176%	$25.6151	$25.62	$25.60	$25.60
Purchase #5	$13.64	10.108%	$15.0187	$15.02	$15.00	$15.00
Purchase #6	$105.84	3.853%	$109.918	$109.92	$109.90	$109.90
Purchase #7	$124.94	12.147%	$140.1165	$140.12	$140.10	$140.10
7 purchase totals =	$612.10		$664.8024	$664.82	$664.75	$664.70