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	$19.45	12.199%	$21.8227	$21.82	$21.80	$21.80
Purchase #2	$139.63	8.781%	$151.8909	$151.89	$151.90	$151.90
Purchase #3	$140.32	9.397%	$153.5059	$153.51	$153.50	$153.50
Purchase #4	$135.77	3.819%	$140.9551	$140.96	$140.95	$141.00
Purchase #5	$106.73	11.340%	$118.8332	$118.83	$118.85	$118.80
Purchase #6	$94.45	4.706%	$98.8948	$98.89	$98.90	$98.90
Purchase #7	$153.94	13.312%	$174.4325	$174.43	$174.45	$174.40
7 purchase totals =	$790.29		$860.3351	$860.33	$860.35	$860.30