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	$95.91	7.396%	$103.0035	$103.00	$103.00	$103.00
Purchase #2	$58.64	12.107%	$65.7395	$65.74	$65.75	$65.70
Purchase #3	$54.86	9.229%	$59.923	$59.92	$59.90	$59.90
Purchase #4	$74.68	4.508%	$78.0466	$78.05	$78.05	$78.00
Purchase #5	$217.38	7.757%	$234.2422	$234.24	$234.25	$234.20
Purchase #6	$10.66	4.728%	$11.164	$11.16	$11.15	$11.20
Purchase #7	$44.82	8.836%	$48.7803	$48.78	$48.80	$48.80
7 purchase totals =	$556.95		$600.8991	$600.89	$600.90	$600.80