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	$179.34	11.496%	$199.9569	$199.96	$199.95	$200.00
Purchase #2	$148.59	3.828%	$154.278	$154.28	$154.30	$154.30
Purchase #3	$16.89	7.113%	$18.0914	$18.09	$18.10	$18.10
Purchase #4	$216.65	10.241%	$238.8371	$238.84	$238.85	$238.80
Purchase #5	$81.81	8.846%	$89.0469	$89.05	$89.05	$89.00
Purchase #6	$229.92	11.222%	$255.7216	$255.72	$255.70	$255.70
Purchase #7	$33.79	12.522%	$38.0212	$38.02	$38.00	$38.00
7 purchase totals =	$906.99		$993.9531	$993.96	$993.95	$993.90