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	$7.85	9.486%	$8.5947	$8.59	$8.60	$8.60
Purchase #2	$159.38	8.591%	$173.0723	$173.07	$173.05	$173.10
Purchase #3	$94.75	6.569%	$100.9741	$100.97	$100.95	$101.00
Purchase #4	$75.61	3.872%	$78.5376	$78.54	$78.55	$78.50
Purchase #5	$225.73	4.354%	$235.5583	$235.56	$235.55	$235.60
Purchase #6	$209.90	13.557%	$238.3561	$238.36	$238.35	$238.40
Purchase #7	$140.93	11.247%	$156.7804	$156.78	$156.80	$156.80
7 purchase totals =	$914.15		$991.8735	$991.87	$991.85	$992.00