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	$214.94	13.227%	$243.3701	$243.37	$243.35	$243.40
Purchase #2	$206.77	8.693%	$224.7445	$224.74	$224.75	$224.70
Purchase #3	$130.46	9.263%	$142.5445	$142.54	$142.55	$142.50
Purchase #4	$156.75	10.636%	$173.4219	$173.42	$173.40	$173.40
Purchase #5	$90.29	6.823%	$96.4505	$96.45	$96.45	$96.50
Purchase #6	$41.62	5.428%	$43.8791	$43.88	$43.90	$43.90
Purchase #7	$90.67	3.132%	$93.5098	$93.51	$93.50	$93.50
7 purchase totals =	$931.50		$1,017.9204	$1,017.91	$1,017.90	$1,017.90