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	$87.66	10.192%	$96.5943	$96.59	$96.60	$96.60
Purchase #2	$242.78	10.617%	$268.556	$268.56	$268.55	$268.60
Purchase #3	$49.27	7.132%	$52.7839	$52.78	$52.80	$52.80
Purchase #4	$33.90	11.186%	$37.6921	$37.69	$37.70	$37.70
Purchase #5	$116.64	6.252%	$123.9323	$123.93	$123.95	$123.90
Purchase #6	$42.63	13.752%	$48.4925	$48.49	$48.50	$48.50
Purchase #7	$141.27	5.815%	$149.4849	$149.48	$149.50	$149.50
7 purchase totals =	$714.15		$777.5360	$777.52	$777.60	$777.60