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	$144.34	13.368%	$163.6354	$163.64	$163.65	$163.60
Purchase #2	$141.27	6.813%	$150.8947	$150.89	$150.90	$150.90
Purchase #3	$106.54	9.717%	$116.8925	$116.89	$116.90	$116.90
Purchase #4	$48.89	5.715%	$51.6841	$51.68	$51.70	$51.70
Purchase #5	$241.87	11.736%	$270.2559	$270.26	$270.25	$270.30
Purchase #6	$133.71	5.848%	$141.5294	$141.53	$141.55	$141.50
Purchase #7	$101.28	13.121%	$114.5689	$114.57	$114.55	$114.60
7 purchase totals =	$917.90		$1,009.4609	$1,009.46	$1,009.50	$1,009.50