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	$50.51	3.725%	$52.3915	$52.39	$52.40	$52.40
Purchase #2	$60.81	3.330%	$62.835	$62.84	$62.85	$62.80
Purchase #3	$48.87	13.217%	$55.3291	$55.33	$55.35	$55.30
Purchase #4	$7.81	8.312%	$8.4592	$8.46	$8.45	$8.50
Purchase #5	$107.90	6.479%	$114.8908	$114.89	$114.90	$114.90
Purchase #6	$125.72	13.442%	$142.6193	$142.62	$142.60	$142.60
Purchase #7	$94.61	11.333%	$105.3322	$105.33	$105.35	$105.30
7 purchase totals =	$496.23		$541.8571	$541.86	$541.90	$541.80