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	$170.76	7.301%	$183.2272	$183.23	$183.25	$183.20
Purchase #2	$51.77	4.402%	$54.0489	$54.05	$54.05	$54.00
Purchase #3	$236.43	4.606%	$247.32	$247.32	$247.30	$247.30
Purchase #4	$131.72	9.261%	$143.9186	$143.92	$143.90	$143.90
Purchase #5	$76.60	12.835%	$86.4316	$86.43	$86.45	$86.40
Purchase #6	$249.56	9.828%	$274.0868	$274.09	$274.10	$274.10
Purchase #7	$113.28	12.395%	$127.3211	$127.32	$127.30	$127.30
7 purchase totals =	$1,030.12		$1,116.3542	$1,116.36	$1,116.35	$1,116.20