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	$179.77	5.180%	$189.0821	$189.08	$189.10	$189.10
Purchase #2	$37.79	12.736%	$42.6029	$42.60	$42.60	$42.60
Purchase #3	$206.55	8.242%	$223.5739	$223.57	$223.55	$223.60
Purchase #4	$187.66	12.452%	$211.0274	$211.03	$211.05	$211.00
Purchase #5	$38.72	7.647%	$41.6809	$41.68	$41.70	$41.70
Purchase #6	$17.48	7.370%	$18.7683	$18.77	$18.75	$18.80
Purchase #7	$71.76	9.671%	$78.6999	$78.70	$78.70	$78.70
7 purchase totals =	$739.73		$805.4354	$805.43	$805.45	$805.50