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	$38.65	10.134%	$42.5668	$42.57	$42.55	$42.60
Purchase #2	$40.42	4.526%	$42.2494	$42.25	$42.25	$42.20
Purchase #3	$240.80	5.822%	$254.8194	$254.82	$254.80	$254.80
Purchase #4	$6.34	8.647%	$6.8882	$6.89	$6.90	$6.90
Purchase #5	$126.85	12.674%	$142.927	$142.93	$142.95	$142.90
Purchase #6	$219.62	11.109%	$244.0176	$244.02	$244.00	$244.00
Purchase #7	$128.98	8.583%	$140.0504	$140.05	$140.05	$140.10
7 purchase totals =	$801.66		$873.5188	$873.53	$873.50	$873.50