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	$150.29	4.382%	$156.8757	$156.88	$156.90	$156.90
Purchase #2	$117.90	7.787%	$127.0809	$127.08	$127.10	$127.10
Purchase #3	$79.50	5.565%	$83.9242	$83.92	$83.90	$83.90
Purchase #4	$23.40	12.458%	$26.3152	$26.32	$26.30	$26.30
Purchase #5	$70.50	11.755%	$78.7873	$78.79	$78.80	$78.80
Purchase #6	$83.30	11.124%	$92.5663	$92.57	$92.55	$92.60
Purchase #7	$224.47	7.659%	$241.6622	$241.66	$241.65	$241.70
7 purchase totals =	$749.36		$807.2118	$807.22	$807.20	$807.30