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	$138.51	10.739%	$153.3846	$153.38	$153.40	$153.40
Purchase #2	$234.57	3.221%	$242.1255	$242.13	$242.15	$242.10
Purchase #3	$104.95	5.789%	$111.0256	$111.03	$111.05	$111.00
Purchase #4	$101.58	11.401%	$113.1611	$113.16	$113.15	$113.20
Purchase #5	$82.29	12.168%	$92.303	$92.30	$92.30	$92.30
Purchase #6	$93.62	9.525%	$102.5373	$102.54	$102.55	$102.50
Purchase #7	$57.65	12.816%	$65.0384	$65.04	$65.05	$65.00
7 purchase totals =	$813.17		$879.5755	$879.58	$879.65	$879.50