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	$166.95	3.691%	$173.1121	$173.11	$173.10	$173.10
Purchase #2	$104.96	4.140%	$109.3053	$109.31	$109.30	$109.30
Purchase #3	$101.56	4.251%	$105.8773	$105.88	$105.90	$105.90
Purchase #4	$104.32	5.872%	$110.4457	$110.45	$110.45	$110.40
Purchase #5	$51.67	5.761%	$54.6467	$54.65	$54.65	$54.60
Purchase #6	$81.39	10.231%	$89.717	$89.72	$89.70	$89.70
Purchase #7	$190.56	5.462%	$200.9684	$200.97	$200.95	$201.00
7 purchase totals =	$801.41		$844.0725	$844.09	$844.05	$844.00