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	$39.96	6.176%	$42.4279	$42.43	$42.45	$42.40
Purchase #2	$246.29	7.622%	$265.0622	$265.06	$265.05	$265.10
Purchase #3	$121.57	7.350%	$130.5054	$130.51	$130.50	$130.50
Purchase #4	$141.89	11.230%	$157.8242	$157.82	$157.80	$157.80
Purchase #5	$162.71	5.338%	$171.3955	$171.40	$171.40	$171.40
Purchase #6	$157.38	5.790%	$166.4923	$166.49	$166.50	$166.50
Purchase #7	$41.43	7.276%	$44.4444	$44.44	$44.45	$44.40
7 purchase totals =	$911.23		$978.1519	$978.15	$978.15	$978.10