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	$157.77	4.277%	$164.5178	$164.52	$164.50	$164.50
Purchase #2	$243.77	12.403%	$274.0048	$274.00	$274.00	$274.00
Purchase #3	$45.95	11.537%	$51.2513	$51.25	$51.25	$51.30
Purchase #4	$71.34	7.214%	$76.4865	$76.49	$76.50	$76.50
Purchase #5	$164.25	12.469%	$184.7303	$184.73	$184.75	$184.70
Purchase #6	$219.56	6.325%	$233.4472	$233.45	$233.45	$233.40
Purchase #7	$179.76	9.163%	$196.2314	$196.23	$196.25	$196.20
7 purchase totals =	$1,082.40		$1,180.6693	$1,180.67	$1,180.70	$1,180.60