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	$38.64	3.775%	$40.0987	$40.10	$40.10	$40.10
Purchase #2	$78.86	5.153%	$82.9237	$82.92	$82.90	$82.90
Purchase #3	$57.57	7.412%	$61.8371	$61.84	$61.85	$61.80
Purchase #4	$71.35	11.228%	$79.3612	$79.36	$79.35	$79.40
Purchase #5	$37.95	3.431%	$39.2521	$39.25	$39.25	$39.30
Purchase #6	$61.69	5.728%	$65.2236	$65.22	$65.20	$65.20
Purchase #7	$146.36	10.869%	$162.2679	$162.27	$162.25	$162.30
7 purchase totals =	$492.42		$530.9643	$530.96	$530.90	$531.00