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	$229.39	12.797%	$258.745	$258.75	$258.75	$258.70
Purchase #2	$40.49	12.525%	$45.5614	$45.56	$45.55	$45.60
Purchase #3	$234.32	6.634%	$249.8648	$249.86	$249.85	$249.90
Purchase #4	$33.56	6.198%	$35.64	$35.64	$35.65	$35.60
Purchase #5	$31.81	3.740%	$32.9997	$33.00	$33.00	$33.00
Purchase #6	$141.55	7.674%	$152.4125	$152.41	$152.40	$152.40
Purchase #7	$111.72	13.666%	$126.9877	$126.99	$127.00	$127.00
7 purchase totals =	$822.84		$902.2111	$902.21	$902.20	$902.20