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	$96.95	3.713%	$100.5498	$100.55	$100.55	$100.50
Purchase #2	$36.43	9.569%	$39.916	$39.92	$39.90	$39.90
Purchase #3	$245.86	12.357%	$276.2409	$276.24	$276.25	$276.20
Purchase #4	$168.32	13.531%	$191.0954	$191.10	$191.10	$191.10
Purchase #5	$113.32	3.748%	$117.5672	$117.57	$117.55	$117.60
Purchase #6	$201.82	10.751%	$223.5177	$223.52	$223.50	$223.50
Purchase #7	$48.51	3.453%	$50.1851	$50.19	$50.20	$50.20
7 purchase totals =	$911.21		$999.0721	$999.09	$999.05	$999.00