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	$28.51	11.165%	$31.6931	$31.69	$31.70	$31.70
Purchase #2	$156.82	10.257%	$172.905	$172.91	$172.90	$172.90
Purchase #3	$75.31	13.715%	$85.6388	$85.64	$85.65	$85.60
Purchase #4	$65.75	13.677%	$74.7426	$74.74	$74.75	$74.70
Purchase #5	$219.72	13.242%	$248.8153	$248.82	$248.80	$248.80
Purchase #6	$205.66	7.700%	$221.4958	$221.50	$221.50	$221.50
Purchase #7	$43.56	7.589%	$46.8658	$46.87	$46.85	$46.90
7 purchase totals =	$795.33		$882.1564	$882.17	$882.15	$882.10