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	$150.74	13.539%	$171.1487	$171.15	$171.15	$171.10
Purchase #2	$103.54	4.396%	$108.0916	$108.09	$108.10	$108.10
Purchase #3	$144.52	11.731%	$161.4736	$161.47	$161.45	$161.50
Purchase #4	$158.79	13.726%	$180.5855	$180.59	$180.60	$180.60
Purchase #5	$101.53	13.436%	$115.1716	$115.17	$115.15	$115.20
Purchase #6	$174.94	12.467%	$196.7498	$196.75	$196.75	$196.70
Purchase #7	$52.63	12.566%	$59.2435	$59.24	$59.25	$59.20
7 purchase totals =	$886.69		$992.4643	$992.46	$992.45	$992.40