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	$230.59	11.436%	$256.9603	$256.96	$256.95	$257.00
Purchase #2	$120.39	9.368%	$131.6681	$131.67	$131.65	$131.70
Purchase #3	$31.88	9.455%	$34.8943	$34.89	$34.90	$34.90
Purchase #4	$154.70	7.621%	$166.4897	$166.49	$166.50	$166.50
Purchase #5	$235.65	8.354%	$255.3362	$255.34	$255.35	$255.30
Purchase #6	$227.67	11.148%	$253.0507	$253.05	$253.05	$253.10
Purchase #7	$149.39	11.842%	$167.0808	$167.08	$167.10	$167.10
7 purchase totals =	$1,150.27		$1,265.4801	$1,265.48	$1,265.50	$1,265.60