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	$102.55	5.104%	$107.7842	$107.78	$107.80	$107.80
Purchase #2	$233.28	13.800%	$265.4726	$265.47	$265.45	$265.50
Purchase #3	$170.80	11.809%	$190.9698	$190.97	$190.95	$191.00
Purchase #4	$102.48	11.502%	$114.2672	$114.27	$114.25	$114.30
Purchase #5	$178.61	6.443%	$190.1178	$190.12	$190.10	$190.10
Purchase #6	$230.44	10.677%	$255.0441	$255.04	$255.05	$255.00
Purchase #7	$34.58	12.610%	$38.9405	$38.94	$38.95	$38.90
7 purchase totals =	$1,052.74		$1,162.5962	$1,162.59	$1,162.55	$1,162.60