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	$77.49	4.798%	$81.208	$81.21	$81.20	$81.20
Purchase #2	$245.35	6.519%	$261.3444	$261.34	$261.35	$261.30
Purchase #3	$118.60	7.469%	$127.4582	$127.46	$127.45	$127.50
Purchase #4	$41.41	10.374%	$45.7059	$45.71	$45.70	$45.70
Purchase #5	$127.77	11.635%	$142.636	$142.64	$142.65	$142.60
Purchase #6	$187.66	12.188%	$210.532	$210.53	$210.55	$210.50
Purchase #7	$133.57	3.739%	$138.5642	$138.56	$138.55	$138.60
7 purchase totals =	$931.85		$1,007.4487	$1,007.45	$1,007.45	$1,007.40