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	$35.71	9.247%	$39.0121	$39.01	$39.00	$39.00
Purchase #2	$56.79	13.527%	$64.472	$64.47	$64.45	$64.50
Purchase #3	$7.27	4.280%	$7.5812	$7.58	$7.60	$7.60
Purchase #4	$68.37	9.320%	$74.7421	$74.74	$74.75	$74.70
Purchase #5	$121.71	4.862%	$127.6275	$127.63	$127.65	$127.60
Purchase #6	$155.44	13.304%	$176.1197	$176.12	$176.10	$176.10
Purchase #7	$76.83	7.842%	$82.855	$82.86	$82.85	$82.90
7 purchase totals =	$522.12		$572.4096	$572.41	$572.40	$572.40