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	$33.78	3.274%	$34.886	$34.89	$34.90	$34.90
Purchase #2	$160.26	7.240%	$171.8628	$171.86	$171.85	$171.90
Purchase #3	$53.77	13.716%	$61.1451	$61.15	$61.15	$61.10
Purchase #4	$150.81	6.772%	$161.0229	$161.02	$161.00	$161.00
Purchase #5	$18.65	6.296%	$19.8242	$19.82	$19.80	$19.80
Purchase #6	$152.39	10.395%	$168.2309	$168.23	$168.25	$168.20
Purchase #7	$189.58	12.497%	$213.2718	$213.27	$213.25	$213.30
7 purchase totals =	$759.24		$830.2437	$830.24	$830.20	$830.20