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	$33.42	7.291%	$35.8567	$35.86	$35.85	$35.90
Purchase #2	$19.55	3.617%	$20.2571	$20.26	$20.25	$20.30
Purchase #3	$121.33	9.723%	$133.1269	$133.13	$133.15	$133.10
Purchase #4	$129.31	6.351%	$137.5225	$137.52	$137.50	$137.50
Purchase #5	$116.52	5.241%	$122.6268	$122.63	$122.65	$122.60
Purchase #6	$65.82	3.187%	$67.9177	$67.92	$67.90	$67.90
Purchase #7	$208.29	6.802%	$222.4579	$222.46	$222.45	$222.50
7 purchase totals =	$694.24		$739.7656	$739.78	$739.75	$739.80