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	$173.43	8.618%	$188.3762	$188.38	$188.40	$188.40
Purchase #2	$200.47	13.187%	$226.906	$226.91	$226.90	$226.90
Purchase #3	$113.78	8.345%	$123.2749	$123.27	$123.25	$123.30
Purchase #4	$210.57	4.312%	$219.6498	$219.65	$219.65	$219.60
Purchase #5	$46.63	13.152%	$52.7628	$52.76	$52.75	$52.80
Purchase #6	$144.87	11.504%	$161.5358	$161.54	$161.55	$161.50
Purchase #7	$97.29	6.359%	$103.4767	$103.48	$103.50	$103.50
7 purchase totals =	$987.04		$1,075.9822	$1,075.99	$1,076.00	$1,076.00