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	$144.46	12.362%	$162.3181	$162.32	$162.30	$162.30
Purchase #2	$237.42	4.706%	$248.593	$248.59	$248.60	$248.60
Purchase #3	$172.79	12.521%	$194.425	$194.43	$194.45	$194.40
Purchase #4	$44.43	5.598%	$46.9172	$46.92	$46.90	$46.90
Purchase #5	$136.94	5.293%	$144.1882	$144.19	$144.20	$144.20
Purchase #6	$56.62	5.565%	$59.7709	$59.77	$59.75	$59.80
Purchase #7	$64.35	3.294%	$66.4697	$66.47	$66.45	$66.50
7 purchase totals =	$857.01		$922.6821	$922.69	$922.65	$922.70