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	$42.98	9.749%	$47.1701	$47.17	$47.15	$47.20
Purchase #2	$103.75	9.614%	$113.7245	$113.72	$113.70	$113.70
Purchase #3	$88.98	12.690%	$100.2716	$100.27	$100.25	$100.30
Purchase #4	$26.81	8.314%	$29.039	$29.04	$29.05	$29.00
Purchase #5	$242.89	12.463%	$273.1614	$273.16	$273.15	$273.20
Purchase #6	$93.82	10.737%	$103.8935	$103.89	$103.90	$103.90
Purchase #7	$153.61	5.511%	$162.0754	$162.08	$162.10	$162.10
7 purchase totals =	$752.84		$829.3355	$829.33	$829.30	$829.40