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	$57.70	6.140%	$61.2428	$61.24	$61.25	$61.20
Purchase #2	$247.71	8.605%	$269.0254	$269.03	$269.05	$269.00
Purchase #3	$196.45	9.823%	$215.7473	$215.75	$215.75	$215.70
Purchase #4	$176.65	11.602%	$197.1449	$197.14	$197.15	$197.10
Purchase #5	$37.61	6.618%	$40.099	$40.10	$40.10	$40.10
Purchase #6	$72.71	13.818%	$82.7571	$82.76	$82.75	$82.80
Purchase #7	$162.67	11.800%	$181.8651	$181.87	$181.85	$181.90
7 purchase totals =	$951.50		$1,047.8816	$1,047.89	$1,047.90	$1,047.80