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	$133.92	12.699%	$150.9265	$150.93	$150.95	$150.90
Purchase #2	$138.65	11.801%	$155.0121	$155.01	$155.00	$155.00
Purchase #3	$110.96	6.587%	$118.2689	$118.27	$118.25	$118.30
Purchase #4	$23.36	8.864%	$25.4306	$25.43	$25.45	$25.40
Purchase #5	$96.59	4.523%	$100.9588	$100.96	$100.95	$101.00
Purchase #6	$127.67	10.760%	$141.4073	$141.41	$141.40	$141.40
Purchase #7	$139.45	7.660%	$150.1319	$150.13	$150.15	$150.10
7 purchase totals =	$770.60		$842.1361	$842.14	$842.15	$842.10