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	$211.59	8.406%	$229.3763	$229.38	$229.40	$229.40
Purchase #2	$231.70	9.633%	$254.0197	$254.02	$254.00	$254.00
Purchase #3	$242.39	12.794%	$273.4014	$273.40	$273.40	$273.40
Purchase #4	$38.55	12.811%	$43.4886	$43.49	$43.50	$43.50
Purchase #5	$51.95	8.501%	$56.3663	$56.37	$56.35	$56.40
Purchase #6	$58.39	5.478%	$61.5886	$61.59	$61.60	$61.60
Purchase #7	$165.70	8.805%	$180.2899	$180.29	$180.30	$180.30
7 purchase totals =	$1,000.27		$1,098.5308	$1,098.54	$1,098.55	$1,098.60