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	$151.45	12.235%	$169.9799	$169.98	$170.00	$170.00
Purchase #2	$57.83	3.644%	$59.9373	$59.94	$59.95	$59.90
Purchase #3	$16.94	13.171%	$19.1712	$19.17	$19.15	$19.20
Purchase #4	$122.78	11.614%	$137.0397	$137.04	$137.05	$137.00
Purchase #5	$108.82	9.468%	$119.1231	$119.12	$119.10	$119.10
Purchase #6	$33.39	3.199%	$34.4581	$34.46	$34.45	$34.50
Purchase #7	$51.85	13.484%	$58.8415	$58.84	$58.85	$58.80
7 purchase totals =	$543.06		$598.5508	$598.55	$598.55	$598.50