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	$12.75	6.390%	$13.5647	$13.56	$13.55	$13.60
Purchase #2	$51.83	9.111%	$56.5522	$56.55	$56.55	$56.60
Purchase #3	$220.65	13.199%	$249.7736	$249.77	$249.75	$249.80
Purchase #4	$152.37	4.718%	$159.5588	$159.56	$159.55	$159.60
Purchase #5	$166.79	8.509%	$180.9822	$180.98	$181.00	$181.00
Purchase #6	$39.39	6.870%	$42.0961	$42.10	$42.10	$42.10
Purchase #7	$149.34	12.759%	$168.3943	$168.39	$168.40	$168.40
7 purchase totals =	$793.12		$870.9219	$870.91	$870.90	$871.10