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	$34.94	5.640%	$36.9106	$36.91	$36.90	$36.90
Purchase #2	$95.56	6.680%	$101.9434	$101.94	$101.95	$101.90
Purchase #3	$223.95	7.358%	$240.4282	$240.43	$240.45	$240.40
Purchase #4	$73.85	10.108%	$81.3148	$81.31	$81.30	$81.30
Purchase #5	$172.59	10.354%	$190.46	$190.46	$190.45	$190.50
Purchase #6	$49.84	3.262%	$51.4658	$51.47	$51.45	$51.50
Purchase #7	$64.88	4.724%	$67.9449	$67.94	$67.95	$67.90
7 purchase totals =	$715.61		$770.4677	$770.46	$770.45	$770.40