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	$122.60	12.252%	$137.621	$137.62	$137.60	$137.60
Purchase #2	$157.35	3.264%	$162.4859	$162.49	$162.50	$162.50
Purchase #3	$208.99	6.619%	$222.823	$222.82	$222.80	$222.80
Purchase #4	$153.91	5.765%	$162.7829	$162.78	$162.80	$162.80
Purchase #5	$59.58	4.432%	$62.2206	$62.22	$62.20	$62.20
Purchase #6	$171.71	8.508%	$186.3191	$186.32	$186.30	$186.30
Purchase #7	$151.90	3.684%	$157.496	$157.50	$157.50	$157.50
7 purchase totals =	$1,026.04		$1,091.7485	$1,091.75	$1,091.70	$1,091.70