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	$104.97	6.450%	$111.7406	$111.74	$111.75	$111.70
Purchase #2	$203.85	6.394%	$216.8842	$216.88	$216.90	$216.90
Purchase #3	$223.30	5.336%	$235.2153	$235.22	$235.20	$235.20
Purchase #4	$102.36	8.803%	$111.3708	$111.37	$111.35	$111.40
Purchase #5	$135.84	6.273%	$144.3612	$144.36	$144.35	$144.40
Purchase #6	$207.80	12.576%	$233.9329	$233.93	$233.95	$233.90
Purchase #7	$42.59	5.510%	$44.9367	$44.94	$44.95	$44.90
7 purchase totals =	$1,020.71		$1,098.4417	$1,098.44	$1,098.45	$1,098.40