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	$206.99	11.692%	$231.1913	$231.19	$231.20	$231.20
Purchase #2	$81.31	3.323%	$84.0119	$84.01	$84.00	$84.00
Purchase #3	$90.32	10.172%	$99.5074	$99.51	$99.50	$99.50
Purchase #4	$63.58	5.524%	$67.0922	$67.09	$67.10	$67.10
Purchase #5	$90.53	10.735%	$100.2484	$100.25	$100.25	$100.20
Purchase #6	$40.59	9.263%	$44.3499	$44.35	$44.35	$44.30
Purchase #7	$30.67	7.243%	$32.8914	$32.89	$32.90	$32.90
7 purchase totals =	$603.99		$659.2925	$659.29	$659.30	$659.20