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	$73.43	11.724%	$82.0389	$82.04	$82.05	$82.00
Purchase #2	$142.67	11.135%	$158.5563	$158.56	$158.55	$158.60
Purchase #3	$33.91	12.622%	$38.1901	$38.19	$38.20	$38.20
Purchase #4	$40.27	5.146%	$42.3423	$42.34	$42.35	$42.30
Purchase #5	$23.96	13.259%	$27.1369	$27.14	$27.15	$27.10
Purchase #6	$36.61	4.395%	$38.219	$38.22	$38.20	$38.20
Purchase #7	$188.63	11.660%	$210.6243	$210.62	$210.60	$210.60
7 purchase totals =	$539.48		$597.1078	$597.11	$597.10	$597.00