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	$177.40	12.792%	$200.093	$200.09	$200.10	$200.10
Purchase #2	$245.85	9.860%	$270.0908	$270.09	$270.10	$270.10
Purchase #3	$30.43	7.742%	$32.7859	$32.79	$32.80	$32.80
Purchase #4	$34.52	7.665%	$37.166	$37.17	$37.15	$37.20
Purchase #5	$243.47	13.848%	$277.1857	$277.19	$277.20	$277.20
Purchase #6	$75.63	12.398%	$85.0066	$85.01	$85.00	$85.00
Purchase #7	$103.52	7.718%	$111.5097	$111.51	$111.50	$111.50
7 purchase totals =	$910.82		$1,013.8377	$1,013.85	$1,013.85	$1,013.90