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	$229.38	12.609%	$258.3025	$258.30	$258.30	$258.30
Purchase #2	$181.81	10.467%	$200.8401	$200.84	$200.85	$200.80
Purchase #3	$141.98	5.565%	$149.8812	$149.88	$149.90	$149.90
Purchase #4	$37.60	8.792%	$40.9058	$40.91	$40.90	$40.90
Purchase #5	$106.94	11.691%	$119.4424	$119.44	$119.45	$119.40
Purchase #6	$128.72	11.815%	$143.9283	$143.93	$143.95	$143.90
Purchase #7	$188.50	9.236%	$205.9099	$205.91	$205.90	$205.90
7 purchase totals =	$1,014.93		$1,119.2102	$1,119.21	$1,119.25	$1,119.10