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	$222.78	3.740%	$231.112	$231.11	$231.10	$231.10
Purchase #2	$67.87	10.381%	$74.9156	$74.92	$74.90	$74.90
Purchase #3	$51.59	5.588%	$54.4728	$54.47	$54.45	$54.50
Purchase #4	$5.78	5.167%	$6.0787	$6.08	$6.10	$6.10
Purchase #5	$21.78	5.856%	$23.0554	$23.06	$23.05	$23.10
Purchase #6	$152.88	10.170%	$168.4279	$168.43	$168.45	$168.40
Purchase #7	$113.38	13.676%	$128.8858	$128.89	$128.90	$128.90
7 purchase totals =	$636.06		$686.9482	$686.96	$686.95	$687.00