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	$53.71	5.811%	$56.8311	$56.83	$56.85	$56.80
Purchase #2	$154.83	10.352%	$170.858	$170.86	$170.85	$170.90
Purchase #3	$219.38	12.308%	$246.3813	$246.38	$246.40	$246.40
Purchase #4	$98.47	5.378%	$103.7657	$103.77	$103.75	$103.80
Purchase #5	$80.88	12.411%	$90.918	$90.92	$90.90	$90.90
Purchase #6	$109.83	6.667%	$117.1524	$117.15	$117.15	$117.20
Purchase #7	$140.45	5.456%	$148.113	$148.11	$148.10	$148.10
7 purchase totals =	$857.55		$934.0195	$934.02	$934.00	$934.10