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	$127.60	11.653%	$142.4692	$142.47	$142.45	$142.50
Purchase #2	$146.61	13.599%	$166.5475	$166.55	$166.55	$166.50
Purchase #3	$103.86	5.596%	$109.672	$109.67	$109.65	$109.70
Purchase #4	$88.58	5.681%	$93.6122	$93.61	$93.60	$93.60
Purchase #5	$211.34	5.682%	$223.3483	$223.35	$223.35	$223.30
Purchase #6	$150.32	8.664%	$163.3437	$163.34	$163.35	$163.30
Purchase #7	$9.79	11.324%	$10.8986	$10.90	$10.90	$10.90
7 purchase totals =	$838.10		$909.8915	$909.89	$909.85	$909.80