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	$30.32	10.152%	$33.3981	$33.40	$33.40	$33.40
Purchase #2	$110.94	8.690%	$120.5807	$120.58	$120.60	$120.60
Purchase #3	$51.82	5.677%	$54.7618	$54.76	$54.75	$54.80
Purchase #4	$53.85	11.240%	$59.9027	$59.90	$59.90	$59.90
Purchase #5	$56.64	4.224%	$59.0325	$59.03	$59.05	$59.00
Purchase #6	$169.60	4.379%	$177.0268	$177.03	$177.05	$177.00
Purchase #7	$228.46	8.133%	$247.0407	$247.04	$247.05	$247.00
7 purchase totals =	$701.63		$751.7433	$751.74	$751.80	$751.70