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	$30.69	7.260%	$32.9181	$32.92	$32.90	$32.90
Purchase #2	$156.91	10.349%	$173.1486	$173.15	$173.15	$173.10
Purchase #3	$8.81	13.457%	$9.9956	$10.00	$10.00	$10.00
Purchase #4	$34.85	4.505%	$36.42	$36.42	$36.40	$36.40
Purchase #5	$97.98	3.376%	$101.2878	$101.29	$101.30	$101.30
Purchase #6	$163.59	9.790%	$179.6055	$179.61	$179.60	$179.60
Purchase #7	$72.40	13.317%	$82.0415	$82.04	$82.05	$82.00
7 purchase totals =	$565.23		$615.4171	$615.43	$615.40	$615.30