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	$172.57	6.557%	$183.8854	$183.89	$183.90	$183.90
Purchase #2	$245.53	5.823%	$259.8272	$259.83	$259.85	$259.80
Purchase #3	$61.62	9.311%	$67.3574	$67.36	$67.35	$67.40
Purchase #4	$100.37	11.283%	$111.6947	$111.69	$111.70	$111.70
Purchase #5	$145.47	3.612%	$150.7244	$150.72	$150.70	$150.70
Purchase #6	$230.61	4.462%	$240.8998	$240.90	$240.90	$240.90
Purchase #7	$11.57	13.873%	$13.1751	$13.18	$13.20	$13.20
7 purchase totals =	$967.74		$1,027.5640	$1,027.57	$1,027.60	$1,027.60