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	$218.99	4.111%	$227.9927	$227.99	$228.00	$228.00
Purchase #2	$208.80	6.443%	$222.253	$222.25	$222.25	$222.30
Purchase #3	$119.82	6.177%	$127.2213	$127.22	$127.20	$127.20
Purchase #4	$90.54	9.869%	$99.4754	$99.48	$99.50	$99.50
Purchase #5	$74.26	7.709%	$79.9847	$79.98	$80.00	$80.00
Purchase #6	$34.76	13.770%	$39.5465	$39.55	$39.55	$39.50
Purchase #7	$35.67	6.571%	$38.0139	$38.01	$38.00	$38.00
7 purchase totals =	$782.84		$834.4875	$834.48	$834.50	$834.50