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	$28.41	8.417%	$30.8013	$30.80	$30.80	$30.80
Purchase #2	$204.75	9.811%	$224.838	$224.84	$224.85	$224.80
Purchase #3	$131.39	7.316%	$141.0025	$141.00	$141.00	$141.00
Purchase #4	$168.80	7.731%	$181.8499	$181.85	$181.85	$181.80
Purchase #5	$239.30	10.667%	$264.8261	$264.83	$264.85	$264.80
Purchase #6	$101.52	9.422%	$111.0852	$111.09	$111.10	$111.10
Purchase #7	$224.59	13.652%	$255.251	$255.25	$255.25	$255.30
7 purchase totals =	$1,098.76		$1,209.6540	$1,209.66	$1,209.70	$1,209.60