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	$210.83	9.869%	$231.6368	$231.64	$231.65	$231.60
Purchase #2	$249.34	12.145%	$279.6223	$279.62	$279.60	$279.60
Purchase #3	$53.98	5.664%	$57.0374	$57.04	$57.05	$57.00
Purchase #4	$182.63	4.519%	$190.883	$190.88	$190.90	$190.90
Purchase #5	$114.69	8.457%	$124.3893	$124.39	$124.40	$124.40
Purchase #6	$85.68	5.388%	$90.2964	$90.30	$90.30	$90.30
Purchase #7	$123.50	10.103%	$135.9772	$135.98	$136.00	$136.00
7 purchase totals =	$1,020.65		$1,109.8424	$1,109.85	$1,109.90	$1,109.80