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	$26.38	9.433%	$28.8684	$28.87	$28.85	$28.90
Purchase #2	$79.43	13.282%	$89.9799	$89.98	$90.00	$90.00
Purchase #3	$117.53	11.798%	$131.3962	$131.40	$131.40	$131.40
Purchase #4	$72.59	11.373%	$80.8457	$80.85	$80.85	$80.80
Purchase #5	$25.41	4.807%	$26.6315	$26.63	$26.65	$26.60
Purchase #6	$61.96	4.286%	$64.6156	$64.62	$64.60	$64.60
Purchase #7	$190.54	13.262%	$215.8094	$215.81	$215.80	$215.80
7 purchase totals =	$573.84		$638.1467	$638.16	$638.15	$638.10