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	$33.68	3.760%	$34.9464	$34.95	$34.95	$34.90
Purchase #2	$32.51	13.559%	$36.918	$36.92	$36.90	$36.90
Purchase #3	$77.52	5.840%	$82.0472	$82.05	$82.05	$82.00
Purchase #4	$58.82	10.741%	$65.1379	$65.14	$65.15	$65.10
Purchase #5	$127.49	5.367%	$134.3324	$134.33	$134.35	$134.30
Purchase #6	$222.32	9.398%	$243.2136	$243.21	$243.20	$243.20
Purchase #7	$213.47	13.618%	$242.5403	$242.54	$242.55	$242.50
7 purchase totals =	$765.81		$839.1358	$839.14	$839.15	$838.90