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	$210.56	3.419%	$217.759	$217.76	$217.75	$217.80
Purchase #2	$177.58	6.696%	$189.4708	$189.47	$189.45	$189.50
Purchase #3	$150.60	10.138%	$165.8678	$165.87	$165.85	$165.90
Purchase #4	$21.62	4.165%	$22.5205	$22.52	$22.50	$22.50
Purchase #5	$120.28	6.315%	$127.8757	$127.88	$127.90	$127.90
Purchase #6	$25.37	9.691%	$27.8286	$27.83	$27.85	$27.80
Purchase #7	$83.37	5.278%	$87.7703	$87.77	$87.75	$87.80
7 purchase totals =	$789.38		$839.0927	$839.10	$839.05	$839.20