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	$5.28	10.340%	$5.826	$5.83	$5.85	$5.80
Purchase #2	$178.93	5.586%	$188.925	$188.93	$188.95	$188.90
Purchase #3	$162.95	5.221%	$171.4576	$171.46	$171.45	$171.50
Purchase #4	$56.28	5.334%	$59.282	$59.28	$59.30	$59.30
Purchase #5	$160.61	6.611%	$171.2279	$171.23	$171.25	$171.20
Purchase #6	$49.39	6.780%	$52.7386	$52.74	$52.75	$52.70
Purchase #7	$28.43	3.536%	$29.4353	$29.44	$29.45	$29.40
7 purchase totals =	$641.87		$678.8924	$678.91	$679.00	$678.80