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	$249.54	13.822%	$284.0314	$284.03	$284.05	$284.00
Purchase #2	$123.58	6.340%	$131.415	$131.42	$131.40	$131.40
Purchase #3	$148.59	11.796%	$166.1177	$166.12	$166.10	$166.10
Purchase #4	$119.64	9.304%	$130.7713	$130.77	$130.75	$130.80
Purchase #5	$38.63	7.106%	$41.375	$41.38	$41.40	$41.40
Purchase #6	$83.84	6.167%	$89.0104	$89.01	$89.00	$89.00
Purchase #7	$170.57	10.397%	$188.3042	$188.30	$188.30	$188.30
7 purchase totals =	$934.39		$1,031.0250	$1,031.03	$1,031.00	$1,031.00