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	$242.82	5.234%	$255.5292	$255.53	$255.55	$255.50
Purchase #2	$10.33	3.580%	$10.6998	$10.70	$10.70	$10.70
Purchase #3	$123.34	6.650%	$131.5421	$131.54	$131.55	$131.50
Purchase #4	$22.27	11.531%	$24.838	$24.84	$24.85	$24.80
Purchase #5	$207.38	8.402%	$224.8041	$224.80	$224.80	$224.80
Purchase #6	$41.64	9.687%	$45.6737	$45.67	$45.65	$45.70
Purchase #7	$213.38	12.611%	$240.2894	$240.29	$240.30	$240.30
7 purchase totals =	$861.16		$933.3763	$933.37	$933.40	$933.30