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	$38.72	9.796%	$42.513	$42.51	$42.50	$42.50
Purchase #2	$32.55	4.264%	$33.9379	$33.94	$33.95	$33.90
Purchase #3	$245.92	6.752%	$262.5245	$262.52	$262.50	$262.50
Purchase #4	$53.38	11.822%	$59.6906	$59.69	$59.70	$59.70
Purchase #5	$110.94	9.331%	$121.2918	$121.29	$121.30	$121.30
Purchase #6	$205.54	9.499%	$225.0642	$225.06	$225.05	$225.10
Purchase #7	$114.75	10.402%	$126.6863	$126.69	$126.70	$126.70
7 purchase totals =	$801.80		$871.7083	$871.70	$871.70	$871.70