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	$48.54	12.115%	$54.4206	$54.42	$54.40	$54.40
Purchase #2	$155.58	6.106%	$165.0797	$165.08	$165.10	$165.10
Purchase #3	$38.67	10.144%	$42.5927	$42.59	$42.60	$42.60
Purchase #4	$166.65	6.697%	$177.8106	$177.81	$177.80	$177.80
Purchase #5	$55.38	4.605%	$57.9302	$57.93	$57.95	$57.90
Purchase #6	$171.46	13.409%	$194.4511	$194.45	$194.45	$194.50
Purchase #7	$52.76	6.569%	$56.2258	$56.23	$56.25	$56.20
7 purchase totals =	$689.04		$748.5107	$748.51	$748.55	$748.50