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	$57.46	6.841%	$61.3908	$61.39	$61.40	$61.40
Purchase #2	$105.30	8.591%	$114.3463	$114.35	$114.35	$114.30
Purchase #3	$86.60	9.718%	$95.0158	$95.02	$95.00	$95.00
Purchase #4	$119.70	12.665%	$134.86	$134.86	$134.85	$134.90
Purchase #5	$142.36	10.296%	$157.0174	$157.02	$157.00	$157.00
Purchase #6	$88.34	13.114%	$99.9249	$99.92	$99.90	$99.90
Purchase #7	$183.43	3.488%	$189.828	$189.83	$189.85	$189.80
7 purchase totals =	$783.19		$852.3832	$852.39	$852.35	$852.30