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	$89.63	12.157%	$100.5263	$100.53	$100.55	$100.50
Purchase #2	$134.29	13.682%	$152.6636	$152.66	$152.65	$152.70
Purchase #3	$72.47	12.290%	$81.3766	$81.38	$81.40	$81.40
Purchase #4	$97.69	6.449%	$103.99	$103.99	$104.00	$104.00
Purchase #5	$187.52	3.235%	$193.5863	$193.59	$193.60	$193.60
Purchase #6	$199.45	13.256%	$225.8891	$225.89	$225.90	$225.90
Purchase #7	$39.77	7.858%	$42.8951	$42.90	$42.90	$42.90
7 purchase totals =	$820.82		$900.9270	$900.94	$901.00	$901.00