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	$246.54	12.311%	$276.8915	$276.89	$276.90	$276.90
Purchase #2	$107.49	6.540%	$114.5198	$114.52	$114.50	$114.50
Purchase #3	$198.91	4.853%	$208.5631	$208.56	$208.55	$208.60
Purchase #4	$63.98	13.234%	$72.4471	$72.45	$72.45	$72.40
Purchase #5	$247.36	6.832%	$264.2596	$264.26	$264.25	$264.30
Purchase #6	$134.86	8.741%	$146.6481	$146.65	$146.65	$146.60
Purchase #7	$12.51	5.481%	$13.1957	$13.20	$13.20	$13.20
7 purchase totals =	$1,011.65		$1,096.5249	$1,096.53	$1,096.50	$1,096.50