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	$181.91	6.418%	$193.585	$193.59	$193.60	$193.60
Purchase #2	$75.51	12.818%	$85.1889	$85.19	$85.20	$85.20
Purchase #3	$63.47	13.326%	$71.928	$71.93	$71.95	$71.90
Purchase #4	$100.93	13.427%	$114.4819	$114.48	$114.50	$114.50
Purchase #5	$154.92	4.574%	$162.006	$162.01	$162.00	$162.00
Purchase #6	$157.40	13.235%	$178.2319	$178.23	$178.25	$178.20
Purchase #7	$32.67	8.534%	$35.4581	$35.46	$35.45	$35.50
7 purchase totals =	$766.81		$840.8798	$840.89	$840.95	$840.90