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	$16.52	5.677%	$17.4578	$17.46	$17.45	$17.50
Purchase #2	$7.95	3.788%	$8.2511	$8.25	$8.25	$8.30
Purchase #3	$174.45	12.206%	$195.7434	$195.74	$195.75	$195.70
Purchase #4	$41.78	13.292%	$47.3334	$47.33	$47.35	$47.30
Purchase #5	$196.49	13.178%	$222.3835	$222.38	$222.40	$222.40
Purchase #6	$101.98	3.792%	$105.8471	$105.85	$105.85	$105.80
Purchase #7	$68.79	4.690%	$72.0163	$72.02	$72.00	$72.00
7 purchase totals =	$607.96		$669.0326	$669.03	$669.05	$669.00