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	$9.79	3.584%	$10.1409	$10.14	$10.15	$10.10
Purchase #2	$114.90	3.193%	$118.5688	$118.57	$118.55	$118.60
Purchase #3	$127.52	11.723%	$142.4692	$142.47	$142.45	$142.50
Purchase #4	$114.44	11.377%	$127.4598	$127.46	$127.45	$127.50
Purchase #5	$100.90	8.378%	$109.3534	$109.35	$109.35	$109.40
Purchase #6	$152.76	8.737%	$166.1066	$166.11	$166.10	$166.10
Purchase #7	$30.51	9.102%	$33.287	$33.29	$33.30	$33.30
7 purchase totals =	$650.82		$707.3857	$707.39	$707.35	$707.50