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	$79.90	10.817%	$88.5428	$88.54	$88.55	$88.50
Purchase #2	$245.93	12.857%	$277.5492	$277.55	$277.55	$277.50
Purchase #3	$167.89	8.828%	$182.7113	$182.71	$182.70	$182.70
Purchase #4	$158.57	9.320%	$173.3487	$173.35	$173.35	$173.30
Purchase #5	$14.75	6.646%	$15.7303	$15.73	$15.75	$15.70
Purchase #6	$178.51	9.848%	$196.0897	$196.09	$196.10	$196.10
Purchase #7	$73.75	13.647%	$83.8147	$83.81	$83.80	$83.80
7 purchase totals =	$919.30		$1,017.7867	$1,017.78	$1,017.80	$1,017.60