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	$134.65	6.706%	$143.6796	$143.68	$143.70	$143.70
Purchase #2	$121.87	9.838%	$133.8596	$133.86	$133.85	$133.90
Purchase #3	$179.64	6.507%	$191.3292	$191.33	$191.35	$191.30
Purchase #4	$127.33	5.225%	$133.983	$133.98	$134.00	$134.00
Purchase #5	$139.27	7.756%	$150.0718	$150.07	$150.05	$150.10
Purchase #6	$168.58	9.372%	$184.3793	$184.38	$184.40	$184.40
Purchase #7	$38.50	5.847%	$40.7511	$40.75	$40.75	$40.80
7 purchase totals =	$909.84		$978.0536	$978.05	$978.10	$978.20