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	$55.92	6.701%	$59.6672	$59.67	$59.65	$59.70
Purchase #2	$176.33	5.811%	$186.5765	$186.58	$186.60	$186.60
Purchase #3	$29.79	9.481%	$32.6144	$32.61	$32.60	$32.60
Purchase #4	$49.51	7.789%	$53.3663	$53.37	$53.35	$53.40
Purchase #5	$80.89	5.340%	$85.2095	$85.21	$85.20	$85.20
Purchase #6	$12.40	13.380%	$14.0591	$14.06	$14.05	$14.10
Purchase #7	$63.84	8.456%	$69.2383	$69.24	$69.25	$69.20
7 purchase totals =	$468.68		$500.7313	$500.74	$500.70	$500.80