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	$36.79	4.551%	$38.4643	$38.46	$38.45	$38.50
Purchase #2	$117.98	11.135%	$131.1171	$131.12	$131.10	$131.10
Purchase #3	$152.80	11.833%	$170.8808	$170.88	$170.90	$170.90
Purchase #4	$100.34	8.617%	$108.9863	$108.99	$109.00	$109.00
Purchase #5	$199.25	8.312%	$215.8117	$215.81	$215.80	$215.80
Purchase #6	$126.54	12.679%	$142.584	$142.58	$142.60	$142.60
Purchase #7	$245.43	10.609%	$271.4677	$271.47	$271.45	$271.50
7 purchase totals =	$979.13		$1,079.3119	$1,079.31	$1,079.30	$1,079.40