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	$178.60	6.113%	$189.5178	$189.52	$189.50	$189.50
Purchase #2	$125.58	11.369%	$139.8572	$139.86	$139.85	$139.90
Purchase #3	$186.52	9.211%	$203.7004	$203.70	$203.70	$203.70
Purchase #4	$244.36	12.803%	$275.6454	$275.65	$275.65	$275.60
Purchase #5	$153.98	6.710%	$164.3121	$164.31	$164.30	$164.30
Purchase #6	$82.68	8.105%	$89.3812	$89.38	$89.40	$89.40
Purchase #7	$141.78	12.240%	$159.1339	$159.13	$159.15	$159.10
7 purchase totals =	$1,113.50		$1,221.5480	$1,221.55	$1,221.55	$1,221.50