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	$13.51	12.501%	$15.1989	$15.20	$15.20	$15.20
Purchase #2	$83.48	11.223%	$92.849	$92.85	$92.85	$92.80
Purchase #3	$242.59	7.720%	$261.3179	$261.32	$261.30	$261.30
Purchase #4	$235.69	12.837%	$265.9455	$265.95	$265.95	$265.90
Purchase #5	$56.48	5.333%	$59.4921	$59.49	$59.50	$59.50
Purchase #6	$72.85	7.675%	$78.4412	$78.44	$78.45	$78.40
Purchase #7	$200.43	11.860%	$224.201	$224.20	$224.20	$224.20
7 purchase totals =	$905.03		$997.4456	$997.45	$997.45	$997.30