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	$16.44	12.264%	$18.4562	$18.46	$18.45	$18.50
Purchase #2	$198.79	10.621%	$219.9035	$219.90	$219.90	$219.90
Purchase #3	$59.35	5.514%	$62.6226	$62.62	$62.60	$62.60
Purchase #4	$154.91	4.646%	$162.1071	$162.11	$162.10	$162.10
Purchase #5	$42.74	12.655%	$48.1487	$48.15	$48.15	$48.10
Purchase #6	$203.67	13.310%	$230.7785	$230.78	$230.80	$230.80
Purchase #7	$53.48	8.247%	$57.8905	$57.89	$57.90	$57.90
7 purchase totals =	$729.38		$799.9071	$799.91	$799.90	$799.90