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	$87.39	13.402%	$99.102	$99.10	$99.10	$99.10
Purchase #2	$213.46	9.311%	$233.3353	$233.34	$233.35	$233.30
Purchase #3	$225.88	12.654%	$254.4629	$254.46	$254.45	$254.50
Purchase #4	$180.45	13.743%	$205.2492	$205.25	$205.25	$205.20
Purchase #5	$204.70	8.223%	$221.5325	$221.53	$221.55	$221.50
Purchase #6	$181.80	8.146%	$196.6094	$196.61	$196.60	$196.60
Purchase #7	$154.81	13.622%	$175.8982	$175.90	$175.90	$175.90
7 purchase totals =	$1,248.49		$1,386.1895	$1,386.19	$1,386.20	$1,386.10