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	$31.56	3.350%	$32.6173	$32.62	$32.60	$32.60
Purchase #2	$57.64	10.738%	$63.8294	$63.83	$63.85	$63.80
Purchase #3	$70.86	10.684%	$78.4307	$78.43	$78.45	$78.40
Purchase #4	$25.36	4.310%	$26.453	$26.45	$26.45	$26.50
Purchase #5	$186.81	4.659%	$195.5135	$195.51	$195.50	$195.50
Purchase #6	$19.31	11.191%	$21.471	$21.47	$21.45	$21.50
Purchase #7	$131.48	10.828%	$145.7167	$145.72	$145.70	$145.70
7 purchase totals =	$523.02		$564.0316	$564.03	$564.00	$564.00