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	$78.38	4.577%	$81.9675	$81.97	$81.95	$82.00
Purchase #2	$183.34	6.719%	$195.6586	$195.66	$195.65	$195.70
Purchase #3	$82.26	9.499%	$90.0739	$90.07	$90.05	$90.10
Purchase #4	$35.27	9.585%	$38.6506	$38.65	$38.65	$38.70
Purchase #5	$48.81	13.723%	$55.5082	$55.51	$55.50	$55.50
Purchase #6	$153.83	10.343%	$169.7406	$169.74	$169.75	$169.70
Purchase #7	$131.63	12.849%	$148.5431	$148.54	$148.55	$148.50
7 purchase totals =	$713.52		$780.1425	$780.14	$780.10	$780.20