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	$178.81	4.765%	$187.3303	$187.33	$187.35	$187.30
Purchase #2	$39.80	7.537%	$42.7997	$42.80	$42.80	$42.80
Purchase #3	$208.96	13.273%	$236.6953	$236.70	$236.70	$236.70
Purchase #4	$67.68	7.820%	$72.9726	$72.97	$72.95	$73.00
Purchase #5	$62.69	5.834%	$66.3473	$66.35	$66.35	$66.30
Purchase #6	$82.36	9.821%	$90.4486	$90.45	$90.45	$90.40
Purchase #7	$78.74	5.264%	$82.8849	$82.88	$82.90	$82.90
7 purchase totals =	$719.04		$779.4787	$779.48	$779.50	$779.40