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	$16.75	7.806%	$18.0575	$18.06	$18.05	$18.10
Purchase #2	$240.79	8.696%	$261.7291	$261.73	$261.75	$261.70
Purchase #3	$87.42	4.669%	$91.5016	$91.50	$91.50	$91.50
Purchase #4	$151.85	3.134%	$156.609	$156.61	$156.60	$156.60
Purchase #5	$181.49	5.144%	$190.8258	$190.83	$190.85	$190.80
Purchase #6	$37.66	11.630%	$42.0399	$42.04	$42.05	$42.00
Purchase #7	$116.55	13.810%	$132.6456	$132.65	$132.65	$132.60
7 purchase totals =	$832.51		$893.4085	$893.42	$893.45	$893.30