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	$42.38	7.538%	$45.5746	$45.57	$45.55	$45.60
Purchase #2	$170.39	13.102%	$192.7145	$192.71	$192.70	$192.70
Purchase #3	$101.43	7.584%	$109.1225	$109.12	$109.10	$109.10
Purchase #4	$104.87	3.316%	$108.3475	$108.35	$108.35	$108.30
Purchase #5	$231.36	3.150%	$238.6478	$238.65	$238.65	$238.60
Purchase #6	$178.28	7.724%	$192.0503	$192.05	$192.05	$192.10
Purchase #7	$237.70	3.108%	$245.0877	$245.09	$245.10	$245.10
7 purchase totals =	$1,066.41		$1,131.5449	$1,131.54	$1,131.50	$1,131.50