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	$45.56	10.151%	$50.1848	$50.18	$50.20	$50.20
Purchase #2	$42.83	10.741%	$47.4304	$47.43	$47.45	$47.40
Purchase #3	$200.62	10.696%	$222.0783	$222.08	$222.10	$222.10
Purchase #4	$45.59	11.246%	$50.7171	$50.72	$50.70	$50.70
Purchase #5	$173.78	12.863%	$196.1333	$196.13	$196.15	$196.10
Purchase #6	$198.95	10.755%	$220.3471	$220.35	$220.35	$220.30
Purchase #7	$132.58	5.630%	$140.0443	$140.04	$140.05	$140.00
7 purchase totals =	$839.91		$926.9353	$926.93	$927.00	$926.80