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	$207.90	6.609%	$221.6401	$221.64	$221.65	$221.60
Purchase #2	$131.39	6.477%	$139.9001	$139.90	$139.90	$139.90
Purchase #3	$129.48	10.146%	$142.617	$142.62	$142.60	$142.60
Purchase #4	$118.75	12.455%	$133.5403	$133.54	$133.55	$133.50
Purchase #5	$91.87	9.476%	$100.5756	$100.58	$100.60	$100.60
Purchase #6	$192.54	9.871%	$211.5456	$211.55	$211.55	$211.50
Purchase #7	$69.73	3.315%	$72.0415	$72.04	$72.05	$72.00
7 purchase totals =	$941.66		$1,021.8602	$1,021.87	$1,021.90	$1,021.70