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	$161.61	6.404%	$171.9595	$171.96	$171.95	$172.00
Purchase #2	$42.71	5.508%	$45.0625	$45.06	$45.05	$45.10
Purchase #3	$129.58	6.274%	$137.7098	$137.71	$137.70	$137.70
Purchase #4	$13.95	6.666%	$14.8799	$14.88	$14.90	$14.90
Purchase #5	$59.68	9.725%	$65.4839	$65.48	$65.50	$65.50
Purchase #6	$242.43	9.539%	$265.5554	$265.56	$265.55	$265.60
Purchase #7	$44.45	9.557%	$48.6981	$48.70	$48.70	$48.70
7 purchase totals =	$694.41		$749.3491	$749.35	$749.35	$749.50