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	$246.53	13.763%	$280.4599	$280.46	$280.45	$280.50
Purchase #2	$40.39	4.818%	$42.336	$42.34	$42.35	$42.30
Purchase #3	$222.25	4.111%	$231.3867	$231.39	$231.40	$231.40
Purchase #4	$165.74	6.343%	$176.2529	$176.25	$176.25	$176.30
Purchase #5	$136.99	11.293%	$152.4603	$152.46	$152.45	$152.50
Purchase #6	$119.52	4.815%	$125.2749	$125.27	$125.25	$125.30
Purchase #7	$9.68	9.620%	$10.6112	$10.61	$10.60	$10.60
7 purchase totals =	$941.10		$1,018.7819	$1,018.78	$1,018.75	$1,018.90