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	$42.89	8.572%	$46.5665	$46.57	$46.55	$46.60
Purchase #2	$195.44	7.133%	$209.3807	$209.38	$209.40	$209.40
Purchase #3	$152.97	3.484%	$158.2995	$158.30	$158.30	$158.30
Purchase #4	$39.50	3.515%	$40.8884	$40.89	$40.90	$40.90
Purchase #5	$238.70	10.432%	$263.6012	$263.60	$263.60	$263.60
Purchase #6	$91.57	10.115%	$100.8323	$100.83	$100.85	$100.80
Purchase #7	$156.76	8.189%	$169.5971	$169.60	$169.60	$169.60
7 purchase totals =	$917.83		$989.1657	$989.17	$989.20	$989.20