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	$13.30	13.289%	$15.0674	$15.07	$15.05	$15.10
Purchase #2	$136.51	3.136%	$140.791	$140.79	$140.80	$140.80
Purchase #3	$46.46	12.687%	$52.3544	$52.35	$52.35	$52.40
Purchase #4	$165.63	11.742%	$185.0783	$185.08	$185.10	$185.10
Purchase #5	$20.99	7.334%	$22.5294	$22.53	$22.55	$22.50
Purchase #6	$176.89	4.688%	$185.1826	$185.18	$185.20	$185.20
Purchase #7	$132.56	7.569%	$142.5935	$142.59	$142.60	$142.60
7 purchase totals =	$692.34		$743.5966	$743.59	$743.65	$743.70