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	$156.77	10.283%	$172.8907	$172.89	$172.90	$172.90
Purchase #2	$128.42	11.684%	$143.4246	$143.42	$143.40	$143.40
Purchase #3	$128.81	6.582%	$137.2883	$137.29	$137.30	$137.30
Purchase #4	$244.69	9.329%	$267.5171	$267.52	$267.50	$267.50
Purchase #5	$82.51	4.651%	$86.3475	$86.35	$86.35	$86.30
Purchase #6	$160.62	12.106%	$180.0647	$180.06	$180.05	$180.10
Purchase #7	$62.83	6.648%	$67.0069	$67.01	$67.00	$67.00
7 purchase totals =	$964.65		$1,054.5398	$1,054.54	$1,054.50	$1,054.50