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	$156.65	7.352%	$168.1669	$168.17	$168.15	$168.20
Purchase #2	$229.59	13.527%	$260.6466	$260.65	$260.65	$260.60
Purchase #3	$133.73	7.206%	$143.3666	$143.37	$143.35	$143.40
Purchase #4	$101.97	11.167%	$113.357	$113.36	$113.35	$113.40
Purchase #5	$82.88	9.457%	$90.718	$90.72	$90.70	$90.70
Purchase #6	$86.62	10.742%	$95.9247	$95.92	$95.90	$95.90
Purchase #7	$154.25	12.263%	$173.1657	$173.17	$173.15	$173.20
7 purchase totals =	$945.69		$1,045.3455	$1,045.36	$1,045.25	$1,045.40