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	$166.50	13.698%	$189.3072	$189.31	$189.30	$189.30
Purchase #2	$202.40	10.619%	$223.8929	$223.89	$223.90	$223.90
Purchase #3	$146.33	13.505%	$166.0919	$166.09	$166.10	$166.10
Purchase #4	$48.35	6.196%	$51.3458	$51.35	$51.35	$51.30
Purchase #5	$69.33	4.688%	$72.5802	$72.58	$72.60	$72.60
Purchase #6	$168.83	10.674%	$186.8509	$186.85	$186.85	$186.90
Purchase #7	$38.86	6.480%	$41.3781	$41.38	$41.40	$41.40
7 purchase totals =	$840.60		$931.4470	$931.45	$931.50	$931.50