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	$225.87	5.157%	$237.5181	$237.52	$237.50	$237.50
Purchase #2	$133.68	8.851%	$145.512	$145.51	$145.50	$145.50
Purchase #3	$80.97	11.851%	$90.5658	$90.57	$90.55	$90.60
Purchase #4	$234.40	6.364%	$249.3172	$249.32	$249.30	$249.30
Purchase #5	$20.30	3.336%	$20.9772	$20.98	$21.00	$21.00
Purchase #6	$57.25	11.616%	$63.9002	$63.90	$63.90	$63.90
Purchase #7	$199.45	11.640%	$222.666	$222.67	$222.65	$222.70
7 purchase totals =	$951.92		$1,030.4565	$1,030.47	$1,030.40	$1,030.50