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	$226.31	9.492%	$247.7913	$247.79	$247.80	$247.80
Purchase #2	$83.77	6.303%	$89.05	$89.05	$89.05	$89.10
Purchase #3	$162.88	13.300%	$184.543	$184.54	$184.55	$184.50
Purchase #4	$89.60	12.454%	$100.7588	$100.76	$100.75	$100.80
Purchase #5	$208.74	6.105%	$221.4836	$221.48	$221.50	$221.50
Purchase #6	$39.96	5.332%	$42.0907	$42.09	$42.10	$42.10
Purchase #7	$95.67	6.103%	$101.5087	$101.51	$101.50	$101.50
7 purchase totals =	$906.93		$987.2261	$987.22	$987.25	$987.30